This kit is made using 1/4" MDF and comes unpainted/unfinished. There are no slots in this kit, I use a good strong glue to assemble. 

Approx measurements:

Shelf: 12" tall x 4" wide 

Napkin holder side pieces: 4 3/4" tall x  6 3/4" wide

There is a spacer provided for the middle of the napkin walls for support.