Hey bro, I think this is a great build/guide. It could use a little smoothing around the edges though, like work on putting in icons and such. But otherwise this is great and I hope you have a chance to check my Teemo guide, and maybe my Trynd one if you play him too. Anyway, +1 from me.

Teemo's AP ratios don't scale well enough to build him full AP. A 14% ratio is utterly bad for any damage. With Ad and As he does what any AD carry should, he hits hard and fast. Teemo just has the upside of also having dots.
And the purpose of getting AS when building AD is so you hit more often.
Also, take into consideration that if teemo has 100 AP he only does 14% more (which is 14 more damage) That doesn't sound like a carry to me. If he has 100 AD he'll hit that much every time, plus the dots.
Thanks for the comment :)

learn about a champion's skills before you make a guide for him...the reason people build him ap/as is because ALL of his abilities scale off of ap. There really is no reason not to...your not forfeiting auto attack strength by building him ap because of his toxic shot. People then add in attack speed to make his toxic shot proc more. Now, if you were to build him ad, what is the purpose of getting any attack speed at all?