Section 19. Manner of doing work or acquiring material

The work of
  construction, reconstruction, alteration, repair or improvement  of  any
  state building, whether constructed or to be constructed, may be done by
  the employment of inmate or outside labor or both and by the purchase of
  materials  in  the open market whenever in the opinion of the department
  having jurisdiction over such building, and the commissioner of  general
  services or his authorized representative, such a course shall be deemed
  advantageous  to  the  state,  and  only  upon  plans and specifications
  prepared by the commissioner of general services,  but  no  compensation
  shall  be  allowed  for  the  employment  of inmate labor except convict
  labor.