You have about 1000 square feet. My hoouse is 2000 square feet in
myrtle Beach, SC and a 2-ton heat pump heats and cools it just fine.
On that basis a 1 ton window unit would do the job for you.
However, if your weather is different than mine, and it probably is,
slightly larger or smaller may be required.
To do a proper load calculation, you also need to know the area of the
windows, which type they are, which way they face, how big the overhang
is and how far above the windows the overhang is. You need the same
thing for doors, except direction is not very important. R-19 in the
walls and ceilings is better than most home shops, so that helps.
Is this a home shop, or a commercial shop?
How many people are in there?
How many, what wattage, and what type of lights?
What type of machinery, how much power does it use, how many pieces of
equipment, what duty cycle and what hours of operation?
What indoor temperature do you need?
Are you running any exhaust fans or makeup air fans? How many and what
How tight is the construction?
Lots of variables involved here. If you size it off Square Feet of
floor space, even if you allow for ceiling height, you may be way off
on your sizing.