Outside, next to the house.

Nice. Yeah, you're golden if you can actually build one. It doesn't take much and a wooden stove is arguably much better. (Electric is just for convenience as burning wood in apartment buildings every Fri and Sat drunk as hell would not be as... convenient.)

Basically just build a small hut with a stove in it, I'm sure you're up for it.

I've been in a sauna we set up on a small island on Midsummer's eve once. Or which my friends had set up a few hours before we got there. You just build a large stack of stones so that it can fit a fire underneath it, set up the tent over it, while keeping the flaps open, then once the fire has been on for a long time and the stones are hot, you douse there fire, ventilate a bit, then close the flaps and that's it. Take a bucket of water and go in and splash the stones.

I'm sure sauna stovetops are available in the US. What isn't? Haha. Kiuas is what it is called in Finnish. That's a specific word for the stove of a sauna — like how spaghetti is a word for a specific type of noodle.

And even if you don't use firewood anywhere else, shouldn't be much of an issue to have a lapful or two somewhere in the garage.

So you know, only your imagination is the limit.

And depending on how far you're gonna put the building, you might want to consider a stove top with a small water reserve on it, so you'll have hot water in the sauna and can mix that with cold water to make something decent temperature bathing water you can wash yourself with. It's so relaxing washing yourself in the gentle heat of a sauna as opposed to standing under a shower — or even worse, under a shower (in a cool bathroom) that's not on because you don't want to waste water.

Like either in a bathroom adjacent to a sauna or in the sauna itself once it's not peak hot. Like if you had a wood heated stove, you stop putting in wood like an hour before you wash yourself, depending on the stove. So you still get nice jälkilöyly (after-löyly), like the heat that's left in the sauna after a hard löyly. Some of these terms aren't as easy to translate as I might have thought. Some connotations are lost. Oh wait no they're not: jälkilöyly, residual heat; tepid heat obtained from the sauna stove (see: kiuas) after the actual bathing.

Just to remind you with a sauna as youre designing it, somewhere to sit outside the sauna is also pretty important, so you can cool off in between löylys. Hot, cool, hot, cool, hot, cool.

If you had like a pond in your yard that'd be perfect. A come plunge from a sauna is very traditional. Rolling around in snow is also traditional, if you're in a state that ever gets snow.

Amazon even sells mobile sauna stove tops in the Ststes, I see. (I put in Idaho as my post code to see what's available in the US.)

So flimsy looking mobile sauna stove tops from like a $100 to gorgeous looking huge ones costing $3000 and more.

Just get searching, I guess. Can't decide for you lol.