I'm having a mandolin custom built and I was wondering what you all think is the best wood for a mandolin to play ITM. I'm looking for something that's rather warm as well. I've heard that both cedar and redwood would work well, but I was wondering what everyone here thought. Thank you!

Most mandolin use the maple/spruce combo. I've been seeing cedar used more and more in instruments for it's warmth. Redwood is a good choice, too. Back/side wood can make a difference, too. Choosing mahogany or walnut over maple will give a warmer tone.

I'm actually helping build my own custom mandolin right now, we're using bearclaw spruce for the top and cocobolo back and sides. Neck is maple. It's hopefully going to be a magnificent instrument.
Here's the photos. Still a lot of work left.
https://www.facebook.com/casey.thomasto ... e=3&__nodl

Even Stefan Sobell eventually gave up using on WRC for mando/cittern tops. The sound was good, but the wood was hard to carve and prone to splitting over time. He eventually got fed up with the warranty claims and switched to red or sitka spruce. The back and sides have a lot less influence on sound. Any of maple, rosewood, or mahogany will do fine, IMO.

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And now there was no doubt that the trees were really moving - moving in and out through one another as if in a complicated country dance. ('And I suppose,' thought Lucy, 'when trees dance, it must be a very, very country dance indeed.')

C.S. Lewis

Sorry, what's WRC?

Western Red cedar
http://www.wood-database.com/western-red-cedar/

Sitka Spruce would probably be a good choice. However, as you are going custom-built, I'd consider any recommendations by your luthier-of-choice to achieve your requirements based on their experience and wood locker.

Western red cedar. Redwood wasn't a lot different, IIRC.

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And now there was no doubt that the trees were really moving - moving in and out through one another as if in a complicated country dance. ('And I suppose,' thought Lucy, 'when trees dance, it must be a very, very country dance indeed.')

C.S. Lewis

Yes. More important than any quality of the wood is your luthier's understanding of how to get the best from that species. Any quality tonewood can sound like whatever you want, if your luthier has the skill and knows what you're after. Asking a good luthier to take a stab at an unfamiliar wood because of what some guy said about it on the internets is a crapshoot. The best you're likely to achieve is an instrument that's only a little worse than his usual fare.

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And now there was no doubt that the trees were really moving - moving in and out through one another as if in a complicated country dance. ('And I suppose,' thought Lucy, 'when trees dance, it must be a very, very country dance indeed.')

C.S. Lewis

I've played a few spruce-topped mandolins but only a couple of cedar-topped, but based on that unscientific sample I do prefer cedar. Here's a video of me playing spruce followed by cedar a few years ago:

https://www.youtube.com/watch?v=FTCPlDWFgXQ

To be fair the spruce topped was a very new instrument (which for spruce often translates to a brasher sound) whereas the cedar a year or so old so a bit more broken in, but I think the sound difference is still valid.

I think the main drawback of cedar is it's more easily marked, easy to rest a plectrum or fingernail a bit too firmly and end up with a small ding. If you like your instruments to remain pristine then spruce may be a better bet.

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Frank sings but Walt Disney.
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I know commercial names for wood can differ from scientific names when it comes to cedar. Mainly, eastern red cedar, which is actually a type of Juniper species. This can lead to a bit of confusion, especially on the internet.

None of the new world cedars are related to the 'true' old-world cedars - (ie, Cedrus - Cedar of Lebanon, Atlas Cedar, Deodar Cedar, etc.), and they're not all related to each other, either.

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And now there was no doubt that the trees were really moving - moving in and out through one another as if in a complicated country dance. ('And I suppose,' thought Lucy, 'when trees dance, it must be a very, very country dance indeed.')

C.S. Lewis

This would be an excellent conversation to have with your luthier. If you trust them enough to have them make your instrument, you should have confidence in their ability to achieve the tone you want. Most of the tone is dependent on their work. What have they suggested?