I agree. I'd suggest that all concerned make a list of suitable/possible subjects for future builds; these can then be posted (as a combined effort, single list), and the one that gets the most votes in the poll will be the next one build, the second highest votes the following one, and so on.
As for how many GB's in a given year, I'd think 4, ie. one per 3 month span, would be enough. Of course, if one build happens to conclude quickly, with all particapnts having finished, ready for voting, then the next one can start earlier, with the possibility of 'squeezing' in a fifth build.
I would think that, with the myriad ideas that are bound to emerge from the thoughts of the members (and suggestions from non-participating members) there will be enough on the list to keep us all going for at least 3 to 4 years!
Gosh, I'll be past retiring age before then! Hang on, I'm already retired early! Oh well!