I was thinking last night, have you looked at doing this with engines as well? You'd need 2 engine models, a atmosphere version with a short bell and a vacuum version with a long engine bell. Then you'd set the diameter of the engine (the height would automatically set based on a ratio) with the engine power being limited by the size and the ISP being limited by the power and the type, with vacuum engines having a higher vacuum ISP but lower power for a set size. Fuel and Oxidizer use are a factor of power and ISP. You could take a step further and generate engine clusters, single, twin, row of three, square of four and cross of five. The clusters would use the same stats as above and scale the engine model down and fit it to a mount plate to give the different clusters. So I guess you would gave 10 set engine models (clusters 1 to five, for both Atmos and Vacuum) with the size scaled depending on the diameter of the engine set in the generator. With both engines and fuel tanks we'd be able to custom design the most efficient booster for any payload!