Hey, sorry for the bad formatting, but I want to deliver a point.
The idea of this build, is increase drow's damage as much as you can in the beginning. This build requires you to abuse the enemy team by attacking and running back. Last hitting for creeps is a must. The idea behind the Wraith Band is to gain 18 damage and attack speed (through agility) for 970 gold which is efficient for the price.
Notice I gave you a choice between which to pick first, Helm of Denom or Power Treads. I usually perfer to break it down like this, if I was doing really well, then ill go power treads. Otherwise, assume I am getting abused and my health is always falling, then I usually go for boots, morbid mask then upgrade boots to power trads and the morbid mask into Helm of Denom. Remember, as soon as you get Helm of Denom, you can start rotating in jungle and lane depending on which is best for you at your current situation. Usually if i noticed my farm is really bad, ill take the morbid mask and jungle.
in #4, I get a shadow blade first. Shadow blade will give you higher chances of attacking and killing enemies, the same time will also give you a very good escape mechanism.
The choice between which to go for first Butterfly or Daedlus is up to you. I usually get Butterfly first if I feel like I am easily killed and need some form of evasion and agility. Remember, Butterfly is also useful for its flutter which gives you 35% bonus speed. That is really useful when your chasing enemies.
Deadlus is great for its crits. Remember you have extreme damage output using drow, so your crits will be massive. Thats why Daedlus is a must. Again, it depends on your current situation. If your owning everyone then go ahead and get Daedlus first.
The situational and extreme late game items are all up to you. I personally perfer to get another Daedlus to increase the chances of getting crits. But I can't denay the usefulness of the other items. Ill leave the pick to you.
For the abilities
I usually maximize MARKSMANSHIP first, the reason is you will gain additional damage, and give all your ranged team the same amount of damage aswell.
I tend to maximize frost arrow second, the reason is, if you noticed that frost arrows at level 1 15% and once fully upgraded, 60%. On the other hand Gust at level 1 silences enemies for 3 seconds at level 1, and once maximize it goes for 6 seconds. The movement slow from the upgrade increase significantly (15-60) which makes a big difference between each level of its upgrade. Remember, at early game, enemy heroes hardly have mana, and abilities to abuse. So their is no need to maximize your silence early. Even if they do, then silencing them for 3 seconds is more then enough for you to pull your moves.
I usually play drow in the lane nearest to the jungle rather than mid. It really depends on your team pick, and who your up against.