I often retro fit ceiling into boats and the two woods I prefer are cedar and white pine. I use these woods because they are light weight, very easy to mill, easy to bend and easy to finish. Cedar can be had in a lot of different colors when a customer wants a smorgasbord or pine if they want light natural or a uniform color stained match.
The general dimensions I use are 2" wide (usually scaled to the boat's other elements) by 1/2" thick. This is very light weight, but stiff enough not to sag between well spaced vertical strips.
For the vertical strips, I use two approaches. One is a blended in strip, the same color as the hull shell or liner. It's also wood, usually pine and glued in position with an adhesive/sealant, so it has some flexibility for expansion, contraction and impacts. This is painted to match the hull or liner and the ceiling is screwed to these, often using tile floor spacers (temporarily) between them, to keep even gaps. The other method is matching or contrasting wood and again I use pine, stained to match if necessary, also glued with an adhesive/sealant to the hull shell/liner. I do this because you can have quite a bit of movement from all these pieces of loosely fitted wood, the hull, the liner and the occasional hard landing on a dock
or rafting. All these situations will test the pull out strength of the ceiling fasteners and the ability of the vertical strips to remain attached to the hull shell/liner. Permit
flexibility or you'll pop fasteners in fairly short order.
for thought . . .