Alex, I respect your ingenuity and passion. The roof sketch apps and services available now are quite accurate. I’ve used them thousands of times and subsequently tested the accuracy based upon ordering materials based upon the dimensions obtained from those reports. They’re relatively cheap and fast.
I’m not trying to discourage you, just present you with reality as I see it. Finding the height between the eave and the ridge, with any reasonable precision, is a non trivial task, especially for a hip roof. Suppose there is a long rafter length, how would you propose obtaining that height difference? How would you propose doing it with roofs such as what I’m showing below?
These types of roof architecture are not at all uncommon. And far from the most challenging. These are roofs my company builds on a weekly basis. Two of those shown were built in the past two weeks (you’re seeing before photos). Again, from what I can understand, a key element in your calculations is to know the difference in height between the eave and ridge. The roof in the last photo I showed you has a minimum of 8 different eave and ridge elevations. I sketched this roof myself using a tool called RoofSnap. Below is one page from the roof report showing the sketch and measurements:
You should also take note of all the overhangs that are involved on a roof such as this. How would you propose to include those in your calculations? They can account for a significant amount of roof area on a roof such as this. This roof ended up being 68 SQ of field shingles, 4.67 SQ of cap and 1.67 SQ of starter. We ordered 70 SQ for the field shingles and the exact amounts I mentioned for cap and starter. I build in a fudge factor because it is better and more cost effective for everyone involved to have a small amount left over than have to run after more materials. Even at a 2 square difference, we’re talking accuracy of about 3%. Reality is, with the fudge factor I use, we were pretty much dead on.
I hope this helps your understanding of what challenges you may be facing.