Capture the builders.
Each team has a certain number of builders, say, 2 (we could cvar it). The goals of the team are to capture every builder, and then demolish the other team's base.
Builders in this have no build timer, so they can very quickly keep a base up. Furthermore, if a team's builder is alive, structures will automatically heal, based on the percentage of builders they have left (both builders = 100% heal rate, 1 builder = 50%)
When a team kills the other team's builder, they get another builder. Effectively one team could go to 4 builders, while the other has none.