How to build a studio from scratch
I agree with Barrie, check out other spaces to decide what you like and don't like about them. In addition to renting out a space to do exactly the kind of shoot you want to do, you should peruse CraigsList. Go check out studio rentals and shares, compare the light, space, flooring, HVAC, etc.
Some general tips: however high you think the ceiling should be, add another 2 feet. Have a grey floor. I have wood floors and I'm always removing red from my product shots and people's legs. Will you use it as a meeting space as well? Will you do your retouching in there? 18' wide is a nice space, my space is about 600 sq. ft. and I can squeeze in 2 setups at once if needed.
Add plenty of electricity. LEDs aren't ready for prime time. If you use hot lights for a video project, computer, hair dryer, curling iron and microwave, you'll blow fuses if unprepared. Female models get cold easily and I find goosebumps distracting. I like the recessed outlets so you can put furniture/equipment right up against the wall. But floor outlets and extensions on wheels from up high also have their places.
There are way too many variables to address until you provide more feedback about what you shoot, cost, building code restrictions, etc.
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