Make up the ridge capping in the same way as the roof beams were made in STEP 9.
Make each one (four altogether) slightly longer than the length of the ridge along each dormer. Cut a 45 degree angle inwards at one end of each piece.
Two of the pieces ONLY will need the end of the point cut off, vertically and directly above the adjacent ridge. See top-right picture below.
Fix the ridge capping to the apex of the roof by nailing through the ridge capping into the roof beam.
First fix in place the two pieces of ridge capping with the points cut off (see picture) and then the other two pieces at right angles.