Acoustic guitars use spruce, because it has an incredible strength to weight ratio, but it is a soft wood, and does not have the strength of most hardwoods. The Arch tops that use it are more acoustics than electrics. If you are making an electric, it will be a disapointment. Certainly, if you want to use an electric bridge or bridge/tailpiece you will need a block of what ever your back wood is right under the area, so you will get none of the resonance of the spruce.
Now, if you are thinking of making a big archtop guitar, well, you are getting yourself into a lot more than you relize. First of all, you are about 90% to be disapointed with your first effort. And that is if you are an experience woodworker. If you are not, then it will take you at least a dozen before you get what you are after. I would HIGHLY advise you make a few flat tops first, and that you START with a kit, such as the ones made by
Stewart MacDonald or
LMI. If that doesn't interest you, at the very least buy a copy of Bob Benedetto's book and video series. Stew Mac has them as a set.
One other thing. Do not for one second imagin you will save any money by building a guitar. I save money by building my own guitars, but that is because I already have a shop which is designed for building guitars, and I have wholesale sources for all my parts and pieces and wood. And really, I lose money when I keep the guitars I make, but that is a whole other issue. You will find, however, that you need to spend a great deal of money on tools, and wood (particularly mahogany) is expensive. Mahogany is VERY expensive right now, and only getting more expensive. The supply is shrinking very fast, and let me tell you that I am very glad to have a large supply of wood which I've had for a long time. (If you are thinking of an archtop guitar, mahogany is also not a very popular wood for archtops, so you are going to spend a lot more money trying to find a suitable piece of wood for the back.)
I don't want to sound like I am discouraging you from building a guitar. I am not. Building guitars is a great hobby, and a lot of fun. I very much encourage you to do it, but you need to do it from a place of information. Go out and buy as many books as you can on the subject, most notably the Cumpiano book "Guitarmaking," for acoustics and Bob Bennedetto's book for archtops. And yes, there is a lot of information on the internet as well, but you must tred softly as not all of it is good. This is also why I encourage you to start with something like the Stew Mac or LMI kits, as they both come with really good instructions and videos (or that is what everyone I know who has used them says). They are great skill builders, which is a very important thing for your first guitar, as you are likely to finish it and think something along the lines of, "well, that could have been better." A kit will also help get the quality of the first one a lot higher.
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