3 improvements to make your budget miter saw work like a pro.

[Toolmaker51]

I'm not a carpenter or cabinetmaker, but to enclose ceiling, it needs sealing off at ends of trusses. The brick walls are capped with 2 x 12 lumber where the trusses rest.
Christofix's miter setup looks ideal, with over a 100 to cut. Original plan was 2 pieces overlapping towards middle for an 'adjustable' width, sealing at face of truss joist. I've measured a few, surprisingly consistent 24" centers and 22.5 space. They must have used a block to gauge that. I'll utilize that and halve work involved.