This build is great because although you don't have boots, you still move rather fast because of Teemo's w passive and active. Not sure how the health goes, but it lets you stay alive very long (if you're still cautious, of course) and the items you purchase for health both have slows, allowing you to slow enemies with both basic attacks and abilities which cause his shrooms to make them even slower which isn't necessary, but it is extremely annoying for anyone who steps on it (enemy-wise of course). The Runaan's Hurricane is great for taking more CS and the attack speed, which i usually see is used on Teemo anyway. The BoRK is for more attack speed, slight life steal and a small amount of AD to make his poison more effective dealing much more damage. Also the CDR is great on the Nasher's Tooth to place more shrooms, more frequently. You may have to ask your jungler for a blue buff because the mana consumption is rather crazy. It pays off though :)