I designed this for my kid's Marklin My World tracks, it should be compatible with Marklin's C-tracks too.
The railroad crossing consists of 2 files, the crossing itself and the inlay. The crossing has to be printed twice on it's (wall) side. It can be slided over the tracks and placed together, you don't need any glue as the tracks will keep them together.
I printed the crossing in grey (for the wall), black (asphalt) and white (road marking) to give it a realistic view.
The inlay should be printed upside down and can be placed in the tracks. I made it so my son can drive his Matchbox type cars oper the rails without any obstruction. They will not bother the train either.
My kid's have already had a lot op playing fun with it...