I changed a door size and every door in the project changed too

You edited the type itself — type edits are global, so every placed instance of that type followed. The rule: always Edit Type → Duplicate… first, name the new type by its size (e.g. 0900 x 2100mm), and only then change Width/Height. Undo your change, duplicate, and resize the copy. Same pattern applies to materials: duplicate first, then set panel/frame/glass materials in the Material Browser. Full steps: Duplicate types doors windows →