40K Game Idea: An Ork-focused RTS (or Turn-Based too I guess) that's 50% combat and 50% weapon/vehicle building.
Gather junk parts from enemy factions you defeat in battle and strap them together to form frankenstein Trukks, Battlewagons, and various types of Dakka. Style points are awarded for how spectacularly you can explode or eviscerate your enemies with them.