In the past I've run across a good number of wooden hot tub plans. Some free, some at a reasonable cost. One was for a square or rectangular tub, very low cost plans, but wouldn't really need plans for something like that, believe it was all or mostly plywood.
And wood-fired heater? Don't recall if I saw plans for one or not. However, there is a company out there that makes them, and I believe the round hot tub parts, you put them together if I recall right. But the heater is pretty simple, just need the right materials, and good welding skills. Can't recall the name just now, all I recall is naked gnomes, hats on, climbing into them. That and some in 2-3 foot of snow, and floating on a lake. I'll see what I can find. That was Snorkel I'm pretty sure, but found the company link, but no nekkid gnomes or lake pics.
Here's a couple that made their own hot tub. Should be ample instructions. But there's a ton of info out there.
Google is our friend.
http://makezine.com/projects/build-a-rustic-cedar-hot-tub-for-under-1000/
