Viz - I
encourage my players to make their own stuff. If they can justify it and it doesn't break anything obvious then great! Proof of this is the Burntek weapons (Brainspiller, ChainSAWs 7 & Vendetta), which are made by Byrn. I re-rendered them but the models and concepts are his. In the past, I would render up models for ideas players had.
You can find blank sheets at the back of the equipment index. There are no rules for making your own, I would say that's up to the GM. Hopefully I've provided enough different examples for a player or GM to make their own.
I'm glad you like the art. For my goal of making Icar look like a commercial game (but be free), I need to ensure that the art is of a high quality. I've started on the redesign of the Havoc but need a burst of evening to get it finished.