Having base cabinets and counter tops in place laid a foundation to build cupboards. I started on the long, curb side over the couch. To define a reference edge a temporary 2x4 was clamped in place.
For make shift scaffolding, pipe clamps served well without any mind of their own. Clamping helped tweak position and orientation, up, down, in, out, back and forth, until it was right. Right meaning (1) level to the floor (2) at the desired height and (3) parallel to the center line. Clamps had one job only: to not move, which they did admirably.
From that reference edge a 1x2 ceiling strip was first placed directly above it. The handy bubble level app on my phone said to bevel the top 6 degrees. Temporary braces held it in position so it could be screwed in place to dry check alignment.
More clamps were added to support a 1x2 wall strip. My phone