Groundwork and access
Excavation, removal of material and access for machinery can have a large effect on the work. A tight or sloping site often needs a different plan from an open garden.
Structure and specification
Pool type, dimensions, depth, finish, filtration, heating and cover choices all affect the scope. A detailed specification makes it easier to understand what is included and what remains optional.
The space around the pool
Paving, drainage, landscaping and the finish around the edge may be separate from the pool build. Ask for these items to be made clear so the project can be considered as a whole.