Building to fit curved walls?

[ArtW]

I just hold stuff against the wall, eyeball it, cut it, and hold it against the wall
if it's close, I install it
My builds look rather sad and comical at the same time
You should see the carport i built
LOL

 

[introverting]

Jed over on the Into The Mystery 13 YouTube channel recently posted some how-to videos about making cabinets and such out of polystyrene; much easier to work with and much lighter.

First video:
Second video:
Examples of finished product: