A google on DIY recumbent bicycle generates a number of sites for the DIYer. 15yrs ago there was a site
(wissel/wizzle ?? or something like that) on which a number of recumbent DIYers posted, not only frames
but windshield making and aero covers and storage options. CF is not out
of the question versus welding up steel tubes. CF is definitely easier than Ti as a material and there is
a lot on youtube about working with CF.
The owner of the old WISiL (WIsconsin-ILlinois) site bought the domain, recumbents.com. Look there and you'll find all of the projects that used to be on WISIL.