Nice idea! First off, always start with a heavy, solid baseplate—ideally a 16×16 or bigger. Layer on a few rows of 2×4 bricks to give the foundation depth. Then, build a lattice of 2×6 or 2×8 plates on top; that’s your load‑bearing skeleton. For the green roof, run a grid of 2×2 plates, then screw in 2×1 bricks on top to spread the weight of soil. You can fill the holes with a lightweight mix or even just place pots on the bricks. Use a bit of white glue at the corners of the plates to lock them together; it helps the structure hold up when you add water. Keep it modular by snapping a few “connector” bricks (maybe 1×4s with a stud on each end) into the walls. That way kids can detach a section, add new solar panels or swap out a rooftop garden without tearing the whole model apart. And if you want to upgrade later, just stack a couple more 2×4s under the old foundation—no need to rebuild. Good luck, and remember: the bigger the bricks, the more your city can actually stand on its own!