when i start the game at top i usually make sure i dont fail, hah but i start off with a nashors tooth for the; Cd reduction, attack speed and AP. I then get a GA for some sustain, this is now about mid game and i get my rabadons for damage, then i move on to my Frozen mallet for a little bit of AD and more health/sustain. I finish my build off with either a malady or a zhonya's for more damage or more damage and sustain.

Pro's
Teemo is a great top and can dominate with his shrooms
he is fairly quick and can kill foes fast
with my build he has a lot of sustainability

Con's
Teemo uses a lot of mana early game (especially right after level 6)
early game is also very squishy
doesn't have much damage until about mid game (with my build)

When farming try to stay ahead of the jungler or other solo top but don't worry to much about the ADC (attack damage carry)