Building a garden has an order, and most of the cost of getting it wrong is hidden. Drainage that was never solved shows up as a failed wall two winters later. A patio built before the grading is settled has to come up again.
So the sequence runs the same way every time. Site preparation first: clearing, grading, and making the water go where it should. Then hardscape, because planting around a finished wall is easier than the reverse. Then the planting itself, placed for the light and the soil it will actually live in. Irrigation goes in laid out by hydrozone, so a lawn and a stand of natives are not sharing a valve and one of them losing.
The company that drew the plan is the company that builds it, which removes the gap where a design gets handed to somebody who was not in the room when it was decided.
The full sequence, from the first visit through to the final walkthrough, is set out on the process page.