The roof  is supplied as that 4th fret and is half-etched across most of its surface leaving only the rain strips on each side. I am so used to having to add rain strips from flattened wire this seems a nice touch.
However, the roof does need to be rolled/formed into shape. This is done by forming the large radius curve first by rolling it with the rain strips facing down and supported on something like a computer mouse mat, using a bar of about 25mm diameter. I use a cut from a curtain rail as the roller. Roll it so that the curve is slightly tighter than the curve on the cab front/back.
The bends at the eaves are then formed by rolling round a rod of about 1.5mm diameter. These bends need to be set back from the edge of the roof by about 2.0mm using the rain strip to very gently pull the roof round this bend. If done correctly it will clip in place. However, remember this is a half-etch and thin, it is very easy to distort the roof especially at the corners.
The roof is now soldered in position aligning the rain strip with the half-etched recess on the top of the cab sides and flush with the top of the cab front/back. There is very little if any overlap at the front or back of the cab and the roof should be filed flat to these surfaces.
The other cab detailing parts are resin and so should be left off until later when the soldering iron is put away and everything is cleaned ready for painting. They all will require glueing to the cab floor.