An architectural system of modular construction for building structures including floor and ceiling rails or stringers forming rectangular floor and ceiling sections in vertical alignment with one another, pedestals adapted to be supported on a structural concrete floor for supporting the floor rails, suspension rods adapted to be hung from a structural concrete ceiling for supporting the ceiling rails and vertical corner posts which may be erected at the corners of any of the vertically aligned floor and ceiling sections to extend between the floor and ceiling rails. Panels for the floor and ceiling are supported in the same plane as the floor and ceiling rails on horizontal flanges extending from the floor and ceiling rails. Thus the panels are disposed adjacent the rails, and do not overly the rails. Partition wall panels may be mounted between the erected corner posts in abutting relation with the floor and ceiling rails for selective partitioning of the floor and ceiling sections. The pedestals are adapted for vertical adjustment from above the floor line without removing the floor panels and the corner posts and partition wall panels can be erected and removed without interference with the floor and ceiling rails and panels to provide for a highly flexible and easily altered modular construction.