A blueprint is a building remembered as instructions rather than as a building. Stand on a parcel, name it, and save — everything standing there becomes a plan, with its shapes, sizes, turns and every painted face.
Arm a plan and the build key raises the whole thing somewhere else. Raising one costs the materials it would have cost to build, and it must fit the allowance of the land you raise it on. The plan is checked in full before a single piece is laid, so you never get half a house.
So the loop is: design free in the workshop, save the plan, raise it at home where it costs. If you would rather not shape prims at all, a plan someone else drew works exactly the same in your hands.
A blueprint is one parcel. Anything of the
same build standing over the line is not in it — you will be told how many
pieces were left behind when you save.