well it kinda seems like a logical solution the cylinder will be your base try get 4 rods and stick em in the bottom part, and the funnel looking thing will be the top get 2 racks one for top and one smaller for the bottom part.
Seems like you already have experience in professional grill making from when you did that at age 4 with your dad in the woods...
But I guess if you want to grill outdoors the classic stone circle with a fire inside and the tray on top would be simpler and less bothersome to transport, while that thing you can build without tools from that pipe would be too risky to fire up on your terrace.