I'm wondering how to calculate roof square footage ...

No, pitch and yaw don't figure into it.  The roof is a series of flat planes and you just add the areas of each plane.

Measure from top peak of roof down to bottom. Do this on each individual section of roof.  Add all sections together. This will give you an estimate of how many square of shingles you are going to need. You may want to add in about 3 to 5 square to cover your starter and ridge.

Yaw sure ?

Probably the easiest way to calculate square footage of a roof is to first measure the perimeter of the structure. Then you need to calculate the rise.

To figure the rise you need a tape measure and at least a 2 ft. level. You can take the measurement either from the roof itself, the roof rafters (inside the attic) or from the rake rafter at the gable end. Measure out one foot, level, and with the tape measure at that point, you will have your rise. If you have an overhang, add that to the equation as well, doubling it for the other sides.

The equation, rise times run, will give you the square of the roof. To figure the rise factor, I use a cheat sheet that I copied from one of my architectural books. Most of these types of books will have the table in it somewhere. To try to calculate this, on the fly, is a real pain; and many contractors can’t do it.

Here’s how it works. If you have a 4 in 12 pitch you would multiply the total square footage by a factor of 1.06. If you have a 12 in 12 pitch (45 deg.) you would multiply by a factor of 1.42. Anything under a 4 in 12 or a 3 in 12 pitch is usually considered a flat roof. For that you’d just calculate the total square footage and just round up the nearest foot.

Hopefully that didn’t screw up all your realities. Hey, engineers are not supposed to make things easier, just more expensive. 

Those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety. – Benjamin Franklin

Probably the easiest way to calculate square footage of a roof is to first measure the perimeter of the structure. Then you need to calculate the rise.

To figure the rise you need a tape measure and at least a 2 ft. level. You can take the measurement either from the roof itself, the roof rafters (inside the attic) or from the rake rafter at the gable end. Measure out one foot, level, and with the tape measure at that point, you will have your rise. If you have an overhang, add that to the equation as well, doubling it for the other sides.

The equation, rise times run, will give you the square of the roof. To figure the rise factor, I use a cheat sheet that I copied from one of my architectural books. Most of these types of books will have the table in it somewhere. To try to calculate this, on the fly, is a real pain; and many contractors can’t do it.

Here’s how it works. If you have a 4 in 12 pitch you would multiply the total square footage by a factor of 1.06. If you have a 12 in 12 pitch (45 deg.) you would multiply by a factor of 1.42. Anything under a 4 in 12 or a 3 in 12 pitch is usually considered a flat roof. For that you’d just calculate the total square footage and just round up the nearest foot.

Hopefully that didn’t screw up all your realities. Hey, engineers are not supposed to make things easier, just more expensive.  :-D

Those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety. – Benjamin Franklin

No pitch and yaw needed. Calculate your footprint size in square footage and multiply by a percentage  to add for the steepness of the roof pitch. The footprint is length by  width at the eaves overhang. ( not the foundation size ) Medium pitched roofs add 6 % to 10% to the footprint size, 11% to 16% for steeper pitches and all the way up to 50% added for a super steep faced pitch, that's like  a church steeple type pitch. If you can walk on it without help it's a medium pitch, If you have to lean over to touch the roof to stay on it  then it's steep and if you slip off even if laying on the roof its very steep. Add 10% for cuts as all roofs are not perfect square shapes and there will be wastes. That's your REAL square footage. Ive been a roofer for 35years, this is the straight goods.