Your own creative plot on the Build Island until the next wipe. Type /island in game to go there.

Inside your dome: free building, noclip and god mode, every door, box and deployable a base design can hold from a picker, and Simple Symmetry for mirrored builds. Your plot is saved when you leave and rebuilt when you come back.

Finished a design? Save it as a Base Architect layout (1 slot included if you're not VIP) and have it built on the mainland at the normal cost, or submit it as a raid base. Nothing built on the island leaves it except the design.