there is an awesome article on building a carbon frame on
sheldonbrown.com if that's what you really want to do.
but for touring I'm not sure if it's a good idea to trust a homemade frame made by a nub, especially a carbon fiber one which is especially prone to sudden failure.
if you really must make one then go with lugged steel. you can buy lugs and tubing in whatever dimensions you need, set them up in a jig, and braze them together. brazing is relatively easy and can be done with a cheap household mapp gas torch,
I think a better way of customizing a frame would be to get a lugged frame that's bigger than you need, remove the excessively long tube(s), shorten them, and then rebraze it without totally disassembling in order to avoid the need for a jig.