I am about to make my attempt at one of these. I am making a modification to the size, I would like to try for more of a full length one as opposed to the 3/4 length. So need to help checking on my math and if I am going about it wrong. I reckon I will keep the width the same as the original plans at 48 inches. But the length I would like to bring out to 70-72ish, I am 5' 10 so I guess 70 should keep my feet covered??

So at 48x70 I am guessing I will need 5 yards of IX. That will provide 3 layers at the 45-48" x 60" and 3 layers at 44-48" x 10". Next for the shell, 1.1 ripstop. I figure I will need 4.5 yards to do both sides and make shock cord channels. That way I can skip the gosgrain. So does this sound about right or am I crazy?? lol Thanks for the help.