New decking is sound, straight and without voids.  The outer edge of the bay roof forms a gutter.  Note outlet near far end of the roof. Also notice the tapering of the gutter to facilitate water flow.

Resin paper should always be used as an underlayment to protect the copper from condensation and abrasion from the thermal movement against the decking.  Resin paper is a non-waterproof underlayment meant to protect the copper, not the structure.

Opposite direction, note the tapering of the gutter stop to nothing at the high end.  Two pans have been formed and their seams fully pre-tinned in order to facilitate soaking the joints full of solder.

Here the two pans are fastened down by the outlet. Fastening is done with copper nails and pre-tinned copper cleats. Note frequency of the cleats. Installation always begins at the low point so that the seams lap from the top down.

Additional pans, soldered as they are installed.  Note the backflashing, up the wall. This will eventually be covered by a copper counter flashing, which is cut into the brick.

Completed, fully soldered, looking away from the outlet.

Completed, looking to the outlet.  Note "lacing" of the solder joints, a building up of solder to insure structural strength and to be sure that the joints are fully soaked with solder. Good solder joints are imperative in all flat seam copper installations.