I made the top center skin assembly first. Just dimpled the skin and attached four pieces.  This was all back riveted.

Then after cleaning up the edges and dimpling the right side top skin, I attached it to the assembly while I did the left top skin. In the last picture the aft fuselage is back up on the table with all the top pieces clecoed in place.  I did this to check the fit of the center top skin at the narrow end. The curve at that end is very tight, and even though I broke the side edges, I use a hand seamer to bend them a little more at that end.