A couple of things come to mind;
Play several guitars with different scale lengths. Gibsons are generally 24-5/8" in actual measurement, some are really the nominal 24-3/4". The Epiphone necks I bought for my project measure slightly more than 24-3/4". "Conversion" necks for Fender guitars are 24-5/8", not the nominal 24-3/4" (this was confirmed to me by both Warmoth and USAG).
Fender's stock scale length is 25-1/2" and that will feel different in terms of roominess. These necks will be readily available, lots of options, reasonable prices.
Pay attention to nut width. I considered putting a 1-3/4" nut width neck on my Mustang at one point because I was finding it cramped even at the first fret. Then I got a CV Tele and it's much more comfortable so the Mustang will remain stock.
Neck profile can make a neck feel smaller than it is. Strange but true.
If you're going to do a custom build, do your homework. Visit GC or some other well-stocked store and try a few and when you find a good fit, research what the specs are for the neck.
.............Bill
