When I first began planning out my level, I decided to design the castle layout.  This was my design process for the layout of the castle:

I began with a simple layout that didn’t include dimensions yet.

I then began experimenting with different potential room dimensions.

The final floor plan that I chose was very similar to my first version.

Here are some screenshots of the model I created.

View down the hallway from the front entrance:

Top View:

Perspective View:

This is what I ultimately created in Maya; however, I realized that an individual level would more practically involve a single room of the castle since the player is a mouse.

After this realization, I created a kitchen floor plan and some other views.

Here is the path the player would take through the kitchen: