Suggestions on Menard's GrandPa's house

Paul, Plastruct makes the type of roof you have for O scale. Only difference is its the real shape. It's very easy to work with, you can cut it, paint it and glue it on. I think it comes two sheets to a package so you would have plenty and it would look better with the real shape. This is a Shell station I scratch built and used the tiles on. Don

Covering with a new roof is a good idea. But to answer about paint, you might try translucent paint for glass or a candy or pearl light(thin) enough  not to have huge impact on the blacks/detail lines (assumed black)

Practice spraying things first as they take more effort to get an even, un-striped coat. (use plenty of distance and smooth even passes without angle or distance changes)

Not about the topic, but I love that Shell station, scale rail, and the evocative photo.

As for the roof, not a whole lot you can do bot wash it down with a transparent stain.