http://forums.dota-allstars.com/index.php?showtopic=133304&st=20&p=1649299&#entry1649299

 The sentinel side boasts great/imbalanced intelligence heroes that can compete with the brute force dominance of the scourge. The sentinel side can rely on Chen the Holy Knight to dominate early games through skillful use of the lvl 2 kobold (speed aura) and the two lvl 5 war stomp creeps (pandaren lvl 5 and centaur khan lvl 5(also provides endurance aura) plus the choice of picking satyr hellcaller lvl 6 who has shockwave and unholy aura(provides regeneration to nearby allies equal to a headdress of rejuvenation and it stacks with it), and Chen also has hand of god as his ultimate which heals all heroes on his team. The Silencer provides global silence(ultimate) and last word aura, which can render combos from heroes such as queen of pain useless, as she is silenced after casting one spell for a few seconds if the silencer is close enough(the silencer is also a good int hero early and late game as he does not rely on spells to deal damage, he does most damage through glaives of wisdom). Another hero who is a staple of sentinel teams is 2HD/THD or otherwise known in full as Twin Head Dragon. THD provides 2 powerful aoe(area of effect) nukes in dual breath and macropyre(ultimate) and a disable in ice path.

The scourge basically uses heroes such as lich and queen of pain at the top lane, lich can harass with frost nova due to dark ritual and queen of pain picks off people from lvl 6 onwards, with her chain combo of shadow strike->blink?->scream of pain->sonic wave. The bottom lane would probably be either pugna with sand king/bane elemental, which can also deal a ton of damage(decrepify+epicenter/(fiends grip and brain sap)+nether blast anyone?)

These agility heroes(mainly melee, esp hunters) would benefit from bracers/wraith bands early game as they have considerably lower hp than melee str heroes. Image heroes SHOULD get diffusal blade/manta style as the feedback(mana burn) effect is the only orb effect that images will be able to utilize fully (full mana burn from images, diffusal burns less than manta style) while certain ranged hunters (such as the aforementioned bone clinkz and viper should get monkey king bar to prevent town portal scrolls from denying them their kills(ever played aiplus and watched as they town portaled away?)

Heroes such as luna moonfang/venomancer could choose to get aghanims scepter to boost their ultimate, or forgo the advantage provided by those two items and go for a battle build (luna should get radiance for a damage item, as other items might make her attack totally disappear and do no damage at all(due to moon glaive), plus her range is so short radiance will still burn creeps ^^, while venomancer could take most damage items, even maelstrom as his poison sting effect lasts very long, the only time the orb effect won’t trigger is when he shoots a chain lightning from maelstrom)

Strength heroes may be further split into two groups, hero killers or tanks or even a supporter(in the case of Omniknight). 

Tanks should focus on getting some hp and damage reduction items such as vanguard, heart of tarrasque and in recent versions the assault cuirass. In order to tank properly, it is imperative that a tank have enough hp AND armor to survive against physical attacks(unless the other team likes to kill “tanks”, then getting a hood of defiance or aegis(older versions) would help out immensely). Having 4000 health and say, 6 armor is not efficient against physical attacks as the tank would be better off having 3000 health and 20 armor or so, since 20 armor gives around 60% resistance to physical attacks, if the opposing team ignores you while you play as a tank, feel free to get a radiance to divert their attention to you.

Strength hero killers (such as the Night Stalker(who has wings but can seem to fly), Slithereen Guard, Spiritbreaker and Bristleback would benefit from damage and attack speed items and maybe 1 or 2 hp boosting items(vanguard normally) or satanic for bristleback(as he has good attack speed from his ultimate for lifestealing sprees)

Spiritbreaker and Slithereen Guard imo would benefit from buying mask of madness and black king bar(activate BKB first then MoM). Slithereen Guard further benefits from MoM as he can activate it if an opponent decides to fight back when he sprints to chase(movement speed is useless in a fight)

some agility heroes such as gondar benefit from buying 3 wraith bands early game since it gives a total of +18 to agi, +9 str and +9 int, which effectively gives 171 bonus hp, 18% bonus attack speed, 18 bonus agi(main stat:agi) plus 2+4/7 armor (every 7 points give 1 to armor) and 117 mana (the bonus hp regen and mana regen is pretty much unimportant as it does not have much effect

This provides the hero with enough mana to use an extra skill (in gondar’s case track and windwalk are free from the mana provided by the wraith bands, thus allowing him to use 2 shuriken tosses in a row track should allow him to chase anyone and hit with one more shuriken toss)

 every wraith band costs 150(slippers of agi)+185(circlet)+125(recipe)=460 gp, 3 wraith bands only cost 1380 gp and provide excellent returns on your minor gold investment for early game power

bracers and nulls are bought for 510 gp each (recipe is 50gp more expensive) bracers are good for providing extra hp since 1 bracer gives 114 bonus hp while nulls provide 78 extra mana (good for heroes with low mana pool and have 3 active skills or have a spammable nuke like chaos knight or luna moonfang)

Let us consider a skill available globally to all heroes of dota: Attribute Bonuses. For the cost of 1 skill point the hero effectively receives +2 to all stats, which is ALSO achievable using 2 ironwood branches. For 114 gp, you are effectively taking 1 lvl of attribute bonus at all times, and since the ironwood branches are dirt cheap, you can sell them off or give them a good whack to destroy them when you do not need them anymore.

Ironwood branches are also used in forming the headdress of rejuvenation and nathrezim buckler (these 2 items can be further combined into mekansm)

It automatically forms itself when you buy these two items, and provides a good boost to certain heroes, such as heroes with low intelligence such as Earthshaker and Moonrider as it provides a static 0.65 mana regen per second(meaning that it gives 0.65 mana regen without taking your intelligence statistic into account, intelligence heroes get more mana regen from Sobi Mask (in fact, any hero that reaches 33 INT and above will get more mana regen than 0.65 per second from the 50% provided by Sobi Mask)

In the most recent Dota version, ring of basilus can be clicked, when it is clicked it changes the aura from +3 armor to surrounding units (including creeps) to a +3 armor to hero only aura (without the +3 armor, creeps will push less further due to the fact that their damage reduction has not been boosted by the + 3 armor aura)

The 0.65 mana regen per second is very handy for teammates and it gives them the mana regen also, and chen especially will benefit from the fact that his creeps will get 0.65 mana regen per second (all neutral creeps have no mana regen normally if i recall correctly)

Pusher heroes such as Keeper of the Light and Prophet will also benefit from buying this nice little item since it increases the armor of their creeps by 3 which increases their survivability

As an additonal boon, ring of basilus provides a decent +6 damage for free

Ring of Basilus can be disassembled or further combined into Vladmir’s Offering

In most competitions(which currently use the most recent stable map, which is 6.37 for now), certain items (such as the very nice Necronomicon(ref:dota-allstars.com)–>or sometimes known as the twin demon summoning book are given a set limit per team to prevent abuse (usually one only is allowed) and Mekansm is mostly given a limit of two.

If a team actually went and bought one necro book each, the other team would actually suffer pretty badly from the 200,300,400 mana burn(hence the recent nerf to 300 mana max) from the necro archer alone, 400 * 5 = 2k mana burnt and the archer also provides endurance aura which gives a small boost to attack and movement speeds, the mana burns alone can prevent any game breaking ultimates from being cast, imagine sand king getting double mana burned for 800 mana = no epicentre = no threat. The necro warrior provides mana burn (it has the same orb effect as magina the anti-mage) and has last word, which does 200,400 and 600 dmg depending on necrobook lvl to the unit that kills it. The two demons have decent damage, with the warrior dealing more damage to heroes due to his normal melee dmg type, while the archer does less damage due to the piercing damage type it has. For reference, normal damage does full damage to hero armor while piercing damage does half damage to heroes (so rhasta’s serpent wards dun really do full damage to a hero unless the hero is voodooed, then the hero will receive full damage as a hero has an armor rating of 0 while polymorphed by guinsoo or voodooed)

http://www.battle.net/war3/basics/armorandweapontypes.shtml

More information regarding damage formulas are available at the link above

http://www.dotaportal.com/index.php?act=items&id=80

up to date stats on necronomicon are available on the above link