The water heater and furnace are fastened in place. The vinyl is then covered with a protective mat or plastic sheeting. Finally, toilets are set in place. At the same time the floor is getting nailed down the exterior and interior walls are being assembled. Like the floor, precut studs are laid out on a jig and nailed in place.
Insulation is unrolled between the studs.
The edges of the studs are coated with liquid glue and precut panels which will become the inside wall of the house stapled into place. Openings for windows and electrical outlets are cut at this time. The entire assembly is lifted with a hoist and moved over to where it can be set onto a floor. You can imagine that an 80' wall made of 2 x 4's butted together has LOTS of flex in it and how straight it becomes depends on the straightness of the floor it is attached to. One of the exterior side walls is lowered into place on a bead of caulk and fastened into place.