I'm looking for an old pc game, 2d strategy with tanks even two leg walkers. You would start every mission with a central building with a builder like a ufo hovering above it. The objective was to destroy the enemy central building and the builder unit. In every map there where factories neutral ones. You would sent the builder to capture the neutral structures which would allow you to produce tanks of various forms. The tanks would be produced indefinetly as long as you controlled the factory.