I've made this mainly for my own use! but if others find it useful, all the better.
A few things to say first.
I'm by no means a pro, this build will not be used by pros, but it works for me.
It's not a serious build, I don't do this to play Teemo optimally, I do it to play him in an interesting way, which also allows me to get kills and help the team.
It's essentially an AP build, of which i'm sure there are many, but its a purely AP build. Turning teemo basicly into a poisony magelike Yordle!
Bottom line; I like this build, it works for me and its fun to play! It is however unfinished, and the order of the items is very open for change and adjustment depending on the individual game youre playing and who youre up against!

I will update this as I get more insight, comments/rating welcome.

*Also if you have any ideas for better items, feel free to comment! I want AP Teemo to be the most badass annoyance in LoL there is :D

*Working out the exact skill usage, basicly you put all your points into the dart, speed and Shrooms.

Happy Shrooming!