I wanted to be able to print in ABS so my first step was to jury-rig a cover (as shown below). It worked but was just a little ugly!
I looked around for after market covers and was surprised at how few are out there. I did finally find the one sold by the "3DPrinterstore24":
Ultitop 1-2 Druckerabdeckung für den Ultimaker 2 C - 3DPrinterstore24.de - DER Onlineshop für 3D-Drucker und Zubehör
They arrived yesterday in a very securely packed box. The instructions were all in German but the pictures made it pretty clear what needed to be done. I would recommend that anyone building this cover insert all the nuts before the parts are assembled. Some will be tight enough to stay in place but others might require a small piece of masking tape. Once the sides start to be put in place I found it a lot harder to insert the securing nuts but this could just be me and my coordination!
The cover and the door look really good mounted on the machine. They look like the were sold by Ultimaker though I suspect that Ultimaker would have used frosted plexi for the side panels! I am very pleased with the cover though.
My only complaint, or suggestion for improvement, would be to either ship the door unassembled but still wrapped in the protective plastic. Or strip the protective plastic before assembling the door. I found it to be a real pain to get the plastic off cleanly and had to partially disassemble the door to do so.