I've sketched out some very rough ideas, but I know some of you have developed some great house build plans.
Anyone care to share pics of what you consider to be excellent double shooting houses? Maybe post a design plan?

Do you know how to frame metal studs? I can send you a set I’ve drawn for a 4x6.

Yes. That would be great. PM heading your way.

When you get it all figured out, I need three. 😁
I prefer them delivered and installed.

I build the walls out of 2x2s (ripped 2x4) and OSB. I build them in panels so I can haul them easy and put them up, screw them together on site. cut slits for windows put the cut pieces back in the holes and hinge from the top. Cord from outside window flap to hole above so I can lift and secure flaps from inside. 4x6 x 6' at front with roof slope to back. Door panel in back. Metal roof.

Mine are 5X8 , windows are 16" tall plexiglass that slide on tracks. Nice carpeted shooting bench across the front . They were site built, 2x4 framed , gabled metal roof , painted exterior plywood outside. Mine have steps with hand rails.

What's the magic window sill height assuming house for kids and adults using old office chairs that may or may not raise and lower?

That may be the most important question of all. You get it 1 or 2” too high and life is miserable. The answer is: 1.5” lower than whatever is currently installed at my club.” LOL

There’s no magic number in my opinion. It’s it’s for kids it’s easier to just find a chair that works. I see them all the time on the side of the road people have set out. I’m definitely not to proud to repurpose someone else’s junk. 😂Just another option.

Just sit on a chair and measure from the ground to your preferred height.

Or get an adjustable office chair. Get it close and use chair as adjustment.

Below 40” for kids.

I built a 5x5 a few years ago. It’s plenty of room for 2 adults. Too me, a 6x6 is too big in cases where you have to look multiple directions. You can’t see out every window from one position so you have too move more.

Build a 2x6 box to recess the windows.

I prefer trap doors. As long as you close them you can keep the rodents out easier.

5x6 is my preferred size for me and 1 kid. I have long legs and hate a box that is only 4' deep, I can't turn in my chair without my knees hitting the wall studs. I have a 6x6 that is also pretty convenient, in that it allows me to scoot to the back wall and stay out of my sons way. I also am able to bring my laptop and get work done in this one while we are getting a hunt in. I just finished a 7x9 that will be in my largest field and should allow me to take all 3 kids when the need arises.

I build all of mine out of whatever material I have readily available. Some are all tin (loud and hot, but will never rot), I have some that are painted plywood and are already starting to show signs of needing attention. I have a couple that are painted OSB they seem to last about the same as the plywood (10 years or so, then start to need attention). My 7'x9' is cedar floored and some of the frame, the walls studs are rough cut heart pine with vinyl siding covering the outside. I prefer plexiglass windows that slide open, shelves in the corners for binos, cups, etc.., carpet on the floor, and a carpeted wide (8-10") shooting shelf at least along the primary shooting window. I have started cutting a V notch in the corner shelves to help hold a rifle barrel so it doesn't fall if bumped. Also I want a door I can walk through, leaning over some is fine, but I do not want to have to crawl in on my hands and knees.

Bambam has brought up a good point. I use to be all on the 5x6 and 5x8 train until decided I couldn't see out of the house very well and deer were running up under my windows in my blind spots. I get mine up high and then you can't see out very well. If it's big and you are having to lean over to see outa the windows not good IMO.

Something to consider. For me it, depends on the placement but bigger isn't necessarily better IMO. I have 4 - 5x8's that I built nearly 20 years ago so if you build it right it isn't cheap but they last. I prefer a 4x6 on 12' legs if hunting by myself the majority of the time. Puts the window over 15'.

And I like wood and heavy built. Sturdier is quieter on average I would say.

I make mine with a full 4' inside dimension x 6' because I am also fairly tall and needed a little extra knee room and the extra 7" is enough. I build mine in 6 pieces, 4 walls, base and roof that can be screwed together on site. Put up base, 4 walls and drop roof over top. I use a trailer door and put rubber stall matting on floor. This is my last build, affectionately known as "the condo".

I think I am going to design one. Which will be a chore, because numbers come easy, carpentry, not so much.

I am not much of a carpenter either but I figured out how to build one so all the pieces fit. I build the base first on the elevator brackets. Then build front wall and attach to base. Side wall gets built straight off the base and front wall and attached. Repeat with other side then same thing on rear.Basically after front wall almost all the measurements come from just marking cut by the base and whatever it attaches too, if that makes any sense. No tape measure needed much. I built one using carpentry and a tape and the pieces did not match up as good as I would have liked. But I can get one tight doing it my way.

Sportsman’s Condo SC-2.......be done with it for years....

I’ve built them on elevator brackets and prefabbed everything in my garage. Took everything to the field and had problems getting everything to match up. Figured out the base was out of square and twisted because the ground wasn’t level. It was a PIA. Next time I’ll be sinking the posts in the ground.