I can't recall which shell I bought, but the roof was covered with fluting, plus there's fluting on the sides, like every other flute, that has to be removed from the windows to the edge of the roof, not for the faint of heart! A small grinder type bit and files work, but take time.
Interior walls were built using sheet stryene, chairs and tables were PSC plastic. Here's some photos:
Formed aluminum ends come with the car as well as a floor, but I made my own. I drew an outline of the shell and cut the ends a tad larger, then sanded/filed them down so they would just slip inside the shell:
The photo is recent, not original end.
I made both floor and ends from 3/16 or 1/4" plastic sheet I got at a local plastics firm, Lowes may carry something.
The first OKE car I got I bought the entire kit, after that I only bought the shell and made the other stuff myself. The ends are kinda plain, now that I have the GDD set I can go back and dress them up.
There's rail inside the shell, you can slide the floor in/out on them. I glued the vestibule end walls in the shell, drilled/tapped holes to match holes drilled in the floor so the floor would stay put. The lounge end was a tight fit in the shell so it can be pulled out. Remove the 2 floor screws at the vestibule end and simply slide out the floor and everything attached to it, just make sure everything attached will clear. I did use the clear plastic sheet OKE provides for the windows, you bow it up inside and friction is suppose to keep it in place.
