"We purchased a building plan that did not include electrical, plumbing, or mechanical layouts. We had a general contractor friend that was helping us with our project (he has since bailed on us). Are we going to have problems finding our own contractors or subcontractors who can install without plans? Thanks, Lisa"
Each of the three home building contractors, electrical contractors, plumbing contractors, and mechanical (HVAC) contractors will design their own layout according to their respective building codes and, in conjunction with your desires for your specific needs.
Each can each give an estimate of cost strictly based on building code compliance to give you a rough estimate for now, along with a list of possible upgrade costs.
Since each of these trades is responsible for not only complying with building codes, but guaranteeing your systems as well, it only makes sense that they design them.
Owner builders have the distinct advantage of having complete control of upgrading systems as their budget and desire permit.
Read my information on contractors and subcontractors starting with How to Find Contractors.
Good luck, Carl Heldmann, byoh.com