Le Corbusier claimed that all the great buildings could be reconstructed from their plans. (He was thinking mostly of his own buildings, but he often used a few classic Greek temples for examples.) You can ascertain the proportioning system that the architects were employing, and so you can figure out the height of the spaces from the plan. You know the materials from the footprint (a block of marble looks like this, a steel column is like that), and you know how how much weight a specific material can hold so you can start to figure out what sort of loads were carried by this plan. He might have been exaggerating to make a point, but his point was that if the design was very honest, the volumes (and therefore the building itself) would be contained in information in the plan.
That seeems correct, appropriate, and a good goal for a building's design.
So we start from the plan. We usually already have some sectional ideas, some ideas about space, spatial vignettes we are interested in, and ideas about the programmatic requirements of the building, but the plan is where we start putting our ideas together, connecting them.
Frank Lloyd Wright felt that the site was where the inspiration lay, so he started by first looking at sections through the site and features of the site that were in plan. We saw a sketch for the last Wright house that he was involved in (just before his death) when we were at the Wright archives in Scottsdale. It was a topographical map and he had just sketched some circles with a soft pencil in loopy configurations following a ridge that was apparent in the topography. So that was where he started: soft shapes (circles) march in plan along a topographical feature (ridge) on the site. He took ill the next day and died in a week or so, but his disciples faithfully followed that little sketch and created another Wright house.
Back to the plan: so if you are looking at the plan, and you start laying down some ideas about the sequence of spaces (our own obsession is often connected to sequence and rhythm), where do you start? Mies liked a grid. Corbusier liked some orthogonal lines that he called regulating lines: often a grid, but often an irregular one with a rhythm like a-b-a-b-c (Mies was stricter about his grids: a-a-a-a-a).
Usually, the site is more interesting than simply an orthogonal grid. The movement of the sun is of particular importance to us (it is the light that creates the experience of the forms built), and so are the relation of prominent landmarks to the site. So, for instance, the Strip is twenty-eight degrees east of north from the Slammer's site. Coincidentally (or perhaps not) the original house was oriented in that direction. So the rest of The Slammer meanders south (to get away from the road, to watch the mountains, to form the courtyard) and while it does so, it steps through those twenty-eight degrees back towards the north south grid (important to the site because it is how the Vegas basin has been etched by the BLM), making a set of seven degree steps. Those same steps allow the building to bend a little this way and that to make the courtyard both a little more intimate and a little more animated than it would be otherwise, and to present a little more imposing face to visitors (a little more aggressive stance in plan). Because that set of rotations starts to affect the cubic volumes we were creating for the programmatic spaces of the house, the house has some more drama, some more movement, than it would otherwise.
The idea which informs those design decisions is a generating geometry. If you saw some of the earliest drawings for the Slammer you would see idealized plans of the courtyard and driveway, sweeping arcs of circles that represented "public" and "private" faces (experiences) of the building. As the generating geometry is added to the mix, and starts to be expressed in the built form, it works off these ideals and that tension creates some of the drama that you feel at The Slammer and in our other work.