HO scale tarpaulin cover to suite existing 3D carriage CAD

I need a model of a realistic tarpaulin cover for the HO scale carraige that I've designed. This item will replace the standard roof in the assembly process, printed separately and slid over the top of the carriage into place. modeller must keep in mind this will be 3D printed hence thicknesses need to be appropriate (not paper thin). 3D can be provided in blender or .stp format. the carriage 3D will be shared at bid acceptance and the usual propriety of information applies. Allow for 1x round of design adjustments after protoype build before final acceptance.