Hi, Tom, you will need a minimum of about 12" - 18" fall on your 20'wide patio,. ok now you have a size to work from, you know how high the front will be so now just add 12"/18" to the back where your roof will fit to the house. fit/work out where you want the support posts ( +/- 9ft between you will have to go to the main vertical studs that are apart of the house screw through the timber,because you will have to take away all the stucco and insulation, down to where you are going to fix the ledger board. now this part of the project is where you pay the big bucks, you will have to get rolls of lead 10" wide ( dont forget the thicker it is the more you will have to pay) so go for the mimimum weight. roll out the lead, and bend it to a slight shape of 4" ( this will be nailed to the ledger board) the rest will/should hand down.now bend this up out of the way for the moment, the main support will be in the 2x12 which will go from the ledger board to the posts. now between the post(or 2x12) fit 3 timbers ( 2x6 from one 2x12 to the other because your sheets ( PVC) run top to bottom so to speak and the 2x6 will run from left to right. this is so you can screw the pvc into place. if you leave about 4' between the 2x6 that should be ok for any snow/heavy rain,.. now that you have finished the framing, and the lead in all ready nailed to the wall plate/ledger board, and its turned up a little. So, what have you got now, you should have your main 2x12 coming from the wall to the posts, between the 2x12 you will have 3 2x6 running the lentgh of the patio,( you can paint them before you fix the pvc, or leave it up to you, now, if youre left handed start to fix the pvc sheets from the left, if your right handed the from the right. screw in the plastic topped screw every 3 to 4 waves/ridges. fix the screws at the top of the ridge/wave, and not in the valley the pvc sheet should be about 1" from the ledger board/wall plate. and at the lower end hang over by about 2"1/2-3" ( dont forget to include the facsha board ( the the board where the gutter is fixed to. because your patio is +/- 50ft I would have two down pipes, one at each end, so your gutter will be at its highest point in the middle( the water will run away in both ways) now its up to you. maybe some one else will give you a better idea off the board. PS: do not at any time walk on the roof, that is why I tell you to fix each panel one at time left to right/ right to left,.... best of luck,,,John 2000
now turn the lead ( the 6" ) up and over the pvc every time you have fix one panel and do this each time as you go along the roof.