Building the wooden frame and decking is no problem. Keep in the back of your mind that a gallon of water weighs about 7 1/2 pounds, the weight of the structure and the amount of people in the tub. So, I am going directly to a very well and stable decking or foundation. Close in your beams close in your joists and tighten up things.
But, if your on a concrete slab, no problem.
Many plans for these tubs and roofs or arbors can be obtained on the Internet by doing a simple search.
Now, the electrical part is crutial. You need a dedicated line from the service box just for this equipment and nothing else on it. Your pulling allot of juice to run the pump, heater, and whatever else you have. Make sure this is done by a good reputable sparky.
Maintain a sliding or hinged or pocket door for access to all your equipment for maintenance and cleaning of filters.
Make sure the tup is not too high for ease in access, or build steps with non skid tops.
Have fun and keep the electricity away from the water.