Pros / Cons
[+]High Attack Speed
[+]Good Snare (If used correctly)
[+]Good Long Range "Nuke"
[-]Squishy (Low Armor and HP)
[-]Low Mana Til Mid Game
[-]Start Getting Focused
[-]No Burst Dmg
First of all I need to stress how important it is that you start with Phase Boots. They will not only help you survive but also give you the extra dmg you need early game. The active also stacks well with your windrun so use if often. I chose the other items mainly because of windrunner's ultimate, Focus Fire. The max attack speed but redused damage works out if you stack alot of dmg and crit. So the main items to focus on are the Crystalys, Orchid Malevolence, and Shadow Blade in whichever order you like best. The early orchid not only gives you a good amount of dmg, int (which is also dmg), attack speed, but also mana which lets you spam power shot. The crystalys is dmg and crit which stacks very well with your ult. By the time you get both items even strenght characters will wonder what is happening when you ult them and their health just drains to nothing. The shadow blade makes you even harder to kill while also giving you a good amound of dmg. Finally I get Mjollnir because of its orb effect which helps in team fights but also gives you so much attack speed that you dont even need to ult anymore. I put the divine rapier on there as the final item, but I would only suggest getting this item if you are making a final push because if you die your team will lose if the oppenents pick up the rapier. Other than that with all the attack speed and crit the +250 dmg will destroy all.
[*] Starting Items
I choose to start with a Sage's Mask, mantle of inteligence and a Tango. The Sage's Mask and mantle of inteligence give you just enough mana regen to let you spam Powershot once in a while to let you last hit and harass the other team. The Tango is for when you are getting harassed back.
[*] Mid Game
Here I try to rush my Phase Boots. It allows windrunner to kite her opponets much easier, to harass and last hit easier, and to catch and kill opponents who try to escape.
After that I focus on getting Crystalys because its easy to build and gets you that fast dmg and crit you really need. The Force Staff is the next obvious choise becasue it gives you dmg, attack speed, a cheap escape and intelligence which adds to your mana. (A secondary choice to this would be a Shadow Blade it gives all of the above minus the intelligence, but instead, it gives you extra dmg upon coming out of the cloak. I would not recomend getting both force stafff and shadow blade as the force staff and phase boots should be all the escape you need.)
If you are having a hard time farming or getting zoned try building a Bracer and Null Talisman to help boost you stats.
[*] Late Game
By this point you should have both the Crystalys and the Force Staff. This is the point you can deviate depending on the situation and personal preferences. I sometimes go for Orchid Malevolence here because it gives plenty of mana plus a lot more dmg and attack speed. However, with the force staff, instead of the shadow blade, you should have sufficient mana and can either go straight into the Daedalus or can get a Helm of the Dominator to help with survivability. I usually focus on finishing the Daedalus because the higher crit and dmg help amazingly with Focus Fire.
Final thing I must say for windrunner players. Always and I say always keep about 100 mana for two reasons. You and your lane partner are fighting the queen of pain is at 80 hp and blinks out. Thankfully you saved 100 mana and now you can Powershot her for the kill. Also you are jungling and you get ganked by sven. As soon as the stun ends you have 100 mana so you can just Windrun out of there.
Hope you have fun playing Windrunner! Please vote for me or give me comments. I am in the process of improving this so suggestions are helpful!