I have a 30x40 and the 30' deep isn't quite wide enough. 36' should be good. The reality is: it won't be enough. Add another 10' and it still will not be enough. That said, build it so it can be added into later. If you end up with a 30x80 or 30x100 in 10-20-30 years. . . So be it.
Stuck by zoning on size Phil, and it fits its location. Starts to drop off at the back, are up against 20' setback to neighbors line on 1 side and other side is the house. Her bra size will never change.