Stage 1:
Arena, large enough for a single fight to take place with entryway on two sides.

Stage 2:
One or two banks of stadium seating on each side.

Stage 3:
Single walls to convert from arena to gatehouse.

Stage 4:
Fighting platforms on defenders side to give some height advantage.

Stage 5:
Reinforced roof and ladders for gatehouse.

Stage 6:
Towers at ends of walls.