This buttress is back in the woods North of the Kanaranzi and Little Ranzi Buttresses. The buttress itself is characterized by a 2 foot to 4 foot roof that spans almost the whole buttress.
Bring medium to large gear for topropes.
Access to the top of the buttress is a pain.
Walk around to the back of the buttress and climb a half dead looking tree up onto the top of the buttress, then climb over the boulder that blocks you access to the toprope setups. Don't do this if you don't feel comfortable soloing very easy climbing - cause that's what you're doing.
The other option is to walk back up on the ridge behind the buttress, and make the 4 foot jump over a 30 foot fall - not recommended! - Be safe!
Mountain Project's determination of some of the classic, most popular, highest rated routes for Flattop Buttress: