Creating things and spaces in Blender is an art. But how to build a small room from a solid object? For example, if you want to make a chamber under the stairs, like the Harry Potter’s room in the first movie, how can you build it? The door shape is usually so odd when it’s down a staircase! Relax, you are going to make it step by step.

Creating an empty room

The first thing you need to have is a basic staircase model that will allow you to create depth inside. Next, you need to create a series of diagonal cuts in the same direction as the stairs. For that, select the two vertices you want to split (one at the top left corner and one from the right down corner), press J to activate the join tool, and look at this new edge just in the middle of the two vertices.

Continue with this process to create a perfect diagonal. But be careful. The first and last columns need to remain without cuts.

Now select the faces that will make up the door of this new room and extrude them back to create a cavity.

Tip: Go to the top orthographic view and insert a Loop Cut according to how you plan to do the thickness of your door. Once you have this, use the Extrude Tool to make a bigger room under the stairs.

Then, duplicate the faces you have already selected by pressing D on your keyboard and putting it right where it starts the hole you just made so that it becomes your door. Don’t forget to use the Extrude Tool to build a more realistic door at the exact size you have done the Loop Cut.

How to separate objects

Now there’s an issue: Because you have created this door from the stairs model, Blender recognizes it as part of the original model (the stairs), and that’s not what you want. To separate two models, you need to:

1. Select the figure, or the group of figures, that you need apart.
2. Press P on your keyboard to bring up the Separate Menu.
3. Pick “Selection”

Even though these new objects are not attached anymore, the pivot point is still located at the same point of the initial model, in this case, the stairs. So, remember to relocate the pivot where you need it for the new object created and separated.

Adding some details

Now, let's go ahead with the shape of the door. Again, you can use the inset tool to create a fancier form than a base door shape.

Note: if you have set the Insert tool as Individual. Don’t worry! Press I again to change it to a Single selection.

Then, extrude and scale the faces to create a sense of depth. Now, if you have set your pivot point and done the cavity inside, you have already finished your Harry Potter’s room!