Concerned about roof trusses and ceiling joists in new-construction home
There is probably a very good reason why this house is sitting there in this unfinished state and up for sale. You should definitely do a detailed investigation of the history surrounding the design, permitting and construction of this house. You may very well find information that would help you understand just what you are getting into should you stay on the path of purchasing this unfinished shell.

The issue that you describe is a very big problem and could very well require removing the roof and replacing the trusses with properly designed assemblies on proper spacing. What may look like a very good deal could end up costing you way more in the long run to get the problems corrected and to pass inspections.