Answer plainly — the designer builds your facility as you go. When it's built you can move rooms, resize them and change anything before you see the plan, Gantt and heat map.
Drag a room to move it, pull a corner to resize it, click one to change its numbers. The operations room is where water starts. When it looks right, see your plan.
+ Room / Copy adds one · Undo / Redo any move or change · ✎ Edit answers (top right) rebuilds from the questions · Snap lines rooms up (hold Alt to place freely)