Tahm Kench scales with AP on most of his abilities (Autos, Q, W, and R). He can work as a good AP 1v1 duelist that has high health and burst damage. Kench is very oppressive early on in lane, this helps give you lane prio for roaming and denying them farm. Tank Kench suffered from a bad late game, this build gives him a way better late game and more carry potential. In team fights, AP Kench is able to provide incredible damage. His Q is good for poking and his W is an absolute nuke when maxed out. His ult is also extremely useful because ,not only can swallow teamates to save them, his ult late game can almost 1 shot anyone. In these team fights he should play like a semi-front line while saving cooldowns for the right moment.

While I have yet to get more experience top lane, I believe mid lane is better overall. Most mages can not avoid Kench's Qs and Ws. Most midlaners are easy to 1v1 and they struggle to get you low health. AP Tahm Kench also has more roam potential in mid lane. Kench can help a lot with his roams because of his W and slows.