It can be a big help to students to plan their museum before beginning their build, and this downloadable grid paper is made in the exact dimensions of the buildable space (49x73).
Tips:
If your students are including accessibility features like elevators, make sure they've planned for it in the blueprint.
Emphasize that the research centre and their museum are two different buildings and they don't have to connect. They can add a nice garden with a path in between them.
For bonus math content, have them calculate the dimensions of each galllery (including surface area and/or volume) and include it on their blueprint.