Continuing with the story:
The majority of projects, the designers end up with detailed plans for the construction of everything (including planting plans or course). These will specify what existing trees are to remain and how they are to be protected during construction, which are to be removed, exactly where artificial pools, rockwork, etc. are to go. It's generally considered impossible to specify in a 2D drawing what artificial trees and rockwork will look like. Sometimes a sketch/drawing is used. Usually a scale model is used. This is considered as though it were a 3D blueprint. Everything is shown on the plans or in the written "specifications" (which may number over a thousand pages of detail): what drinkers are used, the exact substrate of the outdoor holding pens, the types of fencing, etc. All of this is sent out for construction and rockwork fabrication companies to bid on.
In some projects there is a different approach called "design/build." Here, the main contractor and the design team are chosen together and will work together from the start. The contractors will have input into the design with the goal of getting things done faster and cheaper. Later, small parts will be bid out (like landscaping or plumbing) but often contractors were consulted in advance to make sure there will be no surprises later.
Once contracts are awarded, demolition begins.
Once construction starts, everyone is working from the plans. But as the site takes shape, problems arise and opportunities also pop up. Sometimes it may be discovered that as you remove existing soil to the required depth you hit muck and can't just pour a foundation. A new idea is needed. This is gonna cost the zoo (usually). Sometimes, in spite of all the planning, as the site takes shape it's obvious that those big apartment buildings in the distance are not being screened. The designer has to figure out how to screen them. Here, the contractors, landscapers, rockwork fabricators, designers, etc. may all offer ideas. The goal is to look great but not raise the cost of the project.
My favorite experience was when we were building the Congo Gorilla Forest (Bronx Zoo, d'uh!). The design team was all in-house so we were on site every day. Because it was so big a site, the rockwork people were finished in some areas and moving to start others while we were landscaping their initial areas. A fair amount of my landscape was done "on the fly" responding to the site rather than planned in advance on paper as I now have to do. So the placement of trees, vines, etc. was a response to the artificial mudbanks, etc. that had been built. Sometimes while they were working on a stream, I could ask them to add a small planter here or there to make the final effect more realistic. As the rockwork folks saw what I was doing with what they were doing, they changed their plans for the areas they were starting to take advantage of what I could do with them. They remarked that on most jobs, they finish their artificial stuff before landscaping starts and so never get to see how it turns out. So what we had was a sort of live, designing dialogue of trees and gunnite. This almost never happens on projects though, since the designers are usually not on site every day (it would be too expensive).