Decide how much support your roof will need. The larger the roof, the more support required.
Find some beams or sturdy pieces of wood. They need to be anywhere from 2 to 10 feet longer than the height of the roof to the ground. Place them underneath the end of the roof and push them as close to the roof as possible for a tight fit.
Hammer some stakes or small pieces of wood into the ground with a sledgehammer. Watch thumbs and hands while you hammer because a sledgehammer can do some serious damage.
Nail the support beams to the supports in the ground. If the wood fits together tight enough, then you won't have to nail them. By now your roof should have enough support so you can walk underneath it without fear of collapse.
Remove the roof's permanent support. Even though the roof may move a little, there should be no worries about the roof falling on top of you.