Glad this thread has been resurrected and thanks again Marty! I have been carving 'seat of the pants', so every neck is a crap shoot how it will come out. I am going to use this method on my next (and probably thereafter).
I use rough hard maple that is about 1.25" thick. It is called 5/4" at the lumber yard. IF I am doing a rosewood fretboard, I'll prep the neck wood down to 3/4" and use a 1/4" fretboard thickness. I try to keep it at 1" total after sanding, which is within spec. If you come up short you can always make the neck cavity less than 5/8" to compensate, but the beauty of staying within spec means the parts are interchangeable and you can mix and match.
how about the width...for gibson type and tele type?
I don't usually purchase Maple boards wider than 6" for necks. Maple is cheap around here, so I just look for something clear and flatsawn in most cases. For mahogany necks like on a Gibson, I get 12/4 ( 3" thick) stock which will yield quarter sawn necks. The peghead ears are extra pieces glued on to the sides to provide the extra width.