Roofing is easy in sandbox mode pending on your house shape comparing to story mode. Play with the resizing tool and the pitches and the 2 switches for clipping by other rooves in roof edit, I've done a 3 faced gambrel style roof barn, took a lot of work and tweaking but managed to get it where I'm happy with inside and out.

I've been so frustrated by the roofs. Haven't been able to enjoy sandbox mode for this very reason