What I want with this build is to make a hybrid with some AP, lots of AD and nice crit, and lifesteal. This makes my mushrooms hurt more, and makes Teemo available to survive attacks while doing some serious damage to the opponents.

For Runes I use ArmPen, CRD and Crit. I also use ArmPen quintessences.

I start with buying the Vampiric scepter at the start for that lifeleech, so I can stay in lane till I hit level 6. By then I have enough gold to go back and buy me Berserker's Greaves. Next item on the list is the Malady. Now I start farming/ganking my way to the Hextech Gunblade which gives me nice lifesteal/lifeleach + some nice AP/AD. Now I want more speed on his attacks so I buy the Nashors Tooth, which also gives me some more AP + mp5. If the fight lasts long enough I then go for the Infinity Edge + the Phantom Dancer in the end for some more attack speed, AD and lots of nice crit.

For summoner spells I usually take flash (For quick getaways, Teemo is squishy), and exhausts so my enemies won't escape that easily.

I place mushrooms on strategic points, outside Barron and Dragon, and usually make a path between them. I also place mushrooms on our side of the map, so it is easy to see if the enemy is moving behind our lines atempting a gank, or that I block their escape route when they try and run away from me.