I want to do the same thing, only with a hole through the rock so that the water can flow over one side and recirculate. My biggest problem is getting the rock to my back yard because I have to go over my drain field, so I can't use any heavy equipment to move it.

I posted a question about this on Dave's Garden and got some really good responses. The type of rock that I can get from a farm field around here is granite. Two people told me that Granite is hard, but would carve well. You need an angle grinder with a diamond blade. You use the grinder to cut grooves in the rock in a cross hatch pattern, like a giant tic-tac-toe board with lots of squares. Use a chisel to knock out the squares between the grooves. then repeat the process in smaller circles so that the birdbath is deeper in the center than at the edges. At this point, the bottom will have to be smoothed out. I was told that there's a very expensive grinder blade designed for this purpose, but that I could probably use the side of the regular blade to do the same thing. The regular blade isn't designed for this, so it will ruin it quickly and may be dangerous, so this is probably a bad idea. Make sure you wear the proper safety equipment.

Since I haven't done any of this myself, I'm not sure how good this advice is. Maybe someone with more experience can speak up here.

jugglerguy has given good info on how to carve out the rock. I did it one time on a much smaller scale using a hammer and a screwdriver, just chipping the stone away; but the grinder is the way to go. One thing to remember is depending upon the type of rock used, i.e.sandstone for instance, you'll have to apply a sealer in order for the water to remain. Granite? I don't know, maybe one wouldn't need a sealer in that case?

Thank you for the responses. Now all I need is the perfect rock and some time on my hands.

There is a local nursery that sells beautiful rocks of all shapes and sizes, drilled and not drilled, but with slightly polished/smoothed dishes carved out of them. They're beautiful. You may consider looking at local garden centers to see if there's something that catches your eye.

I'd love to see a photo of one of these - they sound fantastic! I'm not sure where I can find something this big, affordable and able for me to transport to my house!

http://vnps.org/living-landscape-summary-rick-darkes-talk/ This guy has a great home done rock birdbath.

Email me I have photography one I made a few days ago miles@safarmer.co.za