Swayback Gable Roof?

[Rich Winsor]

Any ideas how I can create a swayback roof. On our spread here we have a run down ramshackle shack that we euphemistically call the "guest cottage" (see thumbnail). Since I am endeavoring to create a site plan of the whole spread I thought it might be fun to try to add the soon to be demolished "guest cottage" to my plan. So far my feeble attempts to make a roof plane follow a curved path have been to no avail.