On the back side of our house is a concrete pad that is roughly 17'X34'. My wife wants a lean-to built so she can park out of the elements. My question is, is 17' too wide to attempt a lean-to? I have found some plans that can be adapted to fit our space, but the rafters will have to be doubled up to span the 17'. Would there be any issues with building it like this? In my mind I picture 18' long rafters made from 2 sets of 12' and 6' boards nailed together and staggered.

Any help is appreciated!