The first picture is the finished resonator, the second is what I started with (I forgot to take a picture of the ACTUAL guitar I used before cutting it up!). The soundhole covers are drainhole covers, the coverplate is made out of an old metal dish tray, and the bridge covers are two drawer handles. I wimped out on fashioning my own resonator cone/biscuit bridge and tailpiece, and just bought them cheaply online. I also bought a cheap piezo pickup so that the resonator could be amplified.
This is by no means an all inclusive guide to the process I took, more of a rough idea. I kinda just ran with the concept and paid scant attention to precise details...
Step 1: Cutting a Hole in Soundboard, Making the Soundwell
I cut a few arches in the bottom of the "soundwell" so that some noise could escape into the rest of the guitar body. After fitting it in, I applied a heavy dose of wood glue to hold it in place
Step 2: Wood Puttying and Sanding Smooth
Additionally, at this point I cut a new design in the headstock since I didn't like the original shape.
Step 3: A New Cover for the Old Soundhole, Test Placement of Pieces
In order to make sure this wasn't a complete waste of time, I put the resonator cone in and strung it up for a test play. It sounded good, but it was necessary to adjust the string height.
Step 4: Cutting New Soundholes and Coverplate
I used an old metal dish tray (another Goodwill purchase for $2) to cut the new coverplate. In order to get the correct size, I used a piece of cardboard to cut a circle until it covered the hole in the soundboard appropriately, and then traced the circle onto the dish tray. To cut the dish tray, I used cutoff wheels on the dremel tool, and then sanded smooth the cut so that there were no burrs.
I also cut a rectangular hole in the coverplate to account for the bridge. Using a drill, I cut several holes of different sizes in the coverplate.
Step 5: Installing Pickup and Staining
For the stain, I wanted to get a dirty look, so I used a few coats of different color stains. After finishing the staining and applying a coat of polyurethane, I superglued the pickup to the underside of the resonator cone. It ended up dampening the tone quite a bit, but it was nice to be able to plug it into an amp.
Step 6: Applying Soundhole Covers and Coverplate
I attached the bridge covers (two drawer handles) after drilling holes to screw them onto the coverplate. I screwed the coverplate to the guitar body after drilling small holes around the circumference, and then I glued on the piece I made earlier to cover what was left of the old soundhole.
Step 7: Finished!
For a more abbreviated rundown of this process, check out a youtube video I made: