A process for manufacturing a road-bound, horizontally fitted vehicle body with a roof unit having an outer skin and an inward facing ceiling, or an outer skin and an inward facing ceiling with a ceiling frame, whereby the roof unit is a unit ready for installation, and a basic structure having longitudinal frames and side wall columns, the ceiling and the outer skin along with the basic structure having joining configurations that mate with each other at mutual places for joining. The ceiling has at least one fitting from a group of fittings consisting of fittings for a ceiling cover, interior cladding, cushioning against impact, sun shields, an interior rear view mirror, interior lighting, wiring, operating and display elements, sliding, raising, folding, lamellar and glass roofs, and their frame parts and the drive elements, and roof hand grips. The process includes the steps of either inserting the roof unit with the fittings from the front or rear, lowering the roof unit with the fittings or raising the roof unit with the fittings so that mutual configurations for connecting purposes of the roof unit and the basic structure are brought together and joined permanently with each other. The side wall columns of the basic structure have a configuration for connecting purposes and a configuration for connecting to the side wall columns is provided on the ceiling or ceiling frame.