I'd be more inclined to plan how to completely cover the roof, choosing panels accordingly, then sit down with a spreadsheet.
You will inevitably find that panel A at 30c/W fits 37 = 11,234W, panel B is lower power and 40c/W but fits 60 panels = 10900W *and* you can do 5 strings of 12 or something that actually works as an array.
If you like playing with numbers it's great fun :)