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I apologize in advance if this topic has been beaten to death but I really need some input! I've built several guitars and I'd like to try an all mahogany guitar. I have two questions, which type of mahogany is ideal and how thick is the mahogany top, oh and how is the top braced compared to spruce tops? Oops I guess that's three questions. Your feedback is greatly appreciated.

Thanks Todd I really appreciate the input, I'll start looking for for some Honduran mahogany.

...seeing as mahogany isn't as stiff as spruce, i am surprised the bracing wouldn't be heavier, at least the "axial" braces with respect to the strings

edit: not being argumentative as i don't know what i'm talking about when it comes to acoustics, just expressing surprise thats all

Sometimes mahogany is just as stiff as spruce, it's just almost always heavier as well, and therefore not usually the first choice...

Mahogany, like most hardwoods, is stiffer across the grain than spruce. Though the long grain stiffness to density ratio is less than spruce, IMHO the extra cross-grain stiffness is the reason mahogany-topped guitars generally have less extended bass than comparable spruce-topped guitars.
One possible solution is to angle the X-braces and the diagonal braces less (more parallel with the strings).
In studying vintage mahogany-topped Martins (0-17 and 00-17, primarily), I have verified that they are constructed the same as the spruce-topped ones.
I would look for the lowest density mahogany for the top. African (Khaya) and Honduran have similar density numbers in the books, but the actual densities can vary widely. Sapele is noticeably denser, usually.

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John

Generally speaking, mahogany is just as stiff as spruce along the grain, and stiffer across the grain, so a mahogany top will need to be roughly the same thickness as spruce, with roughly the same bracing. It will be heavier, because spruce DOES have a higher stiffness to weight ratio than mahogany.
As others have said, finding a light (low density) piece will serve you best.

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A man hears what he wants to hear, and disreguards the rest. Paul Simon

I agree, Honduran would probably be best. Look for a low density, low damping set. Some thunk, others ring.

What size of guitar are you building? Thickness will depend on that as well as the stiffness and density of your specific set... as has been said, probably about the same thickness to spruce, but it will be heavier.

You can also go thinner and brace differently, to get the weight down. I've done one rosewood top guitar like that, which sounds great, but is dying a slow death of underbracing. I need to do another before I can say for sure that they can sound good and live long, but I'm pretty sure the answer is yes. And that means mahogany should be a walk in the park to get the weight down into the same range as spruce, if desired. The main thing I'd do is fan bracing in the lower bout instead of diagonals. Better support behind the bridge, and lower cross grain stiffness to offset the high cross grain of mahogany. Light weight bridge, too. Not ebony, and taper the thickness so there's no unnecessary weight on the belly end... only the leading edge really needs to be tall, to support the saddle.

For ukuleles the consensus of builders is that mahogany tops need to be thinner than spruce or cedar. I build spruce 10-15% thicker, and cedar about 20% thicker. My test is the longitudinal flexing, which I want to feel to be about the same for each soundboard (no measurements, I'm afraid, just going on feel).

Can't say whether this translates to guitars, or if so how to do the translation. But I believe I've read that Martin mahogany tops from the 30s were noticeably thinner than spruce tops.

I'm leaning towards an all mahogany Parlor, thanks for the input.

Thank you everyone for the input it's greatly appreciated!

In that case, the weight may be a good thing Lower resonant frequency for given stiffness, and still really low weight overall just by virtue of the size.

If you don't have a good top picked out already, I have one that should be great for it. Got it from Hibdon a couple years ago when they were selling second grade stuff for cheap. Has a big drying check that goes through both plates, which limits the usable width. Probably could get an OM out of it, but I can't tell exactly how deep the check goes so I'd superglue it for that to be sure. But a parlor should be totally safe. Low damping and feels pretty light to my hands, although I haven't measured the density.