A useful gazebo estimate starts with the way the backyard works now. Photos can show the relation between the house, pool, patio, fence line, and open yard. Rough measurements are helpful, but so are the details that are harder to put on a plan: where guests naturally gather, where the sun becomes uncomfortable, which route you take from the kitchen, and what part of the property is currently being ignored.
It also helps to decide what needs to happen under the roof. A table for six needs a different footprint than a pair of lounge chairs. A poolside retreat needs clear room for people moving around wet surfaces. A space for hosting may need the gazebo to relate to a deck, bar, or grill area without blocking the paths people use. Starting with the intended use makes it easier to arrive at a size and placement that will still feel right after the novelty wears off.
When you are ready to talk through the project, bring inspiration images if you have them, along with the practical things you want the finished space to solve. The goal is a covered outdoor place that looks right, feels comfortable, and gives your household a reason to use more of the yard.