You might check out this forum
You are being redirected.... It is the homebuilder's sub-forum at that site.
I wish you good luck. There's a lot to getting a bike that works and handles well at higher speeds. Steering is critical. The only person I know who has built his own recumbent bike is a close friend who is a medical doctor. He thought it would be fun to try and used plans and a partial setup from a company no longer in business. The bike was beautiful but on its maiden voyage, the frame broke at the bottom bracket. He wasn't going fast so was unhurt. He repaired the weakness but lost faith in the bike and it has hung from the ceiling of his garage for about 15 years. He went on to buy a long wheelbase bike and a trike.