>>2937959 (OP)
A planter box? You can even build it up higher by putting 2x4's to whatever length you need and outer frames and then nail up a sheet of plywood in-between the frames. Don't know if your condo/apt board will allow any of that so ask them first their rules.
Pallet wood is free fyi, most people will beg you to take them away. Problem is they're heavy as hell so you will have to disassemble it on site into raw wood pieces that you can then transport in your vehicle and then assemble and nail together in whatever shape/format you want at your place.
There are those plastic lattice criss-cross pieces often used in gardens that you could zip-tie up as a frame to then attach coroplast (lawn sign) sheets via zip tie too. They're flimsy but waterproof. Depends on your weather but they won't last through several serious thunderstorm winds. You can attach solar lights to them if you want a bit of cool factor.
