I want to build something scifi for this build as well, so a 15mm slum it is. I really like building these :)
Also, recycling is fun. The top of a horse trailer I once glued some bits on to try and make something to set next to a 28mm house, but since discarded. A very old Tau drone conversion, and some more bits. have to make a barn, a small garden plot, maybe try and tie in the old Necron scarab somehow?
I have less than a month, so carry on.