Welding in a roll cage with a roof still on is very simple . Wot you do is put the main hoop in And the front bars tack them all together then you cut a hole next to the hoop then you put a ratchet strap on the hoop and pull it together so the hoop drops throw the holes witch as the cage is lower in the car it gives you the room to weld the top of the cage . Then lift the cage back up undo the strap and weld the floor up job done