The present invention relates to a composite rail profile, comprising at least two rails, each rail comprising a running surface overhanging on an upright base plate reinforced by a bottom flange, wherein the running surface is suitable for supporting a number of wheeled sliding hatches, wherein each rail is made of extruded aluminum, wherein two composite rail profiles and the sliding hatches together form a sliding roof of a fixed structure, wherein the bottom flange comprises a recess, which recess is provided at an end of the bottom flange for connecting two adjacent rails in parallel. The invention also relates to an assembly and a method for assembling a composite rail profile for mobile support of a number of wheeled sliding hatches.