The modular winerack is designed for 6mm whiteboard, but can be tweaked for other material thicknesses. It is easy to assemble with no glue required to hold it together.
The winerack comes with two types of connectors: narrow single slot for either top or bottom and wide double slot for connecting two modules together into a bigger winerack. Each module fits on 1 x P3, and if you're making more than one module for stacking, you should delete the connectors off the second files, as they will be surplus. If you only want the one module, you should delete the surplus double slot connectors.