There are a few programs out there that let you build sets using the ldraw spec. A good place to start is https://www.ldraw.org/ https://www.ldraw.org/ https:

There are a few programs out there that let you build sets using the ldraw spec. A good place to start is https://www.ldraw.org/ https://www.ldraw.org/ https://www.ldraw.org/downloads-2/third-party-software.html https://www.ldraw.org/downloads-2/third-party-software.html They had plugins for awhile that exported to 3d programs (blender, pov, etc) for awhile if I remember correctly. There are also links to semi reasonable CAD style programs. There is another editor someone recently came out with (the name escapes me at the moment) that looks very promising. I would combine the ldraw programs with sites like brickset and others to get the exact pieces in the sets I knew I owned. That way I could build things in 3d then build them for real. I think one of the programs I used had a instruction builder too that you could print out.