When creating things in a 3D environment, you must think about the essential elements that compose your scene. In a room, you will need doors and windows, otherwise, that would be a cage. So let’s learn how to make windows in a 3D indoor space.

The first concern could be how to create a glass? Well if you don’t need look outside, you can use a plane. Remember: A plane is like a single flat face. So once you have it, scale it and set it on the wall.

Note: Use the Wireframe Mode and Top Orthographic View (press seven (7) on your keyboard to set it just in the middle of the hole.

Now let’s make a frame around the window:

1. Create a Cube and scale it in Edit mode.
2. Place the cube in one of the corners you have on the wall destined for the window.
3. Press G on your keyboard to create a large rectangle, the same size as the window hole.
4. Put this rectangle in the middle between the intersection of the wall and the hollow.
5. Use the Extrude Tool to complete the Framework around.

When you have finished extruding, notice that the final part is separated from the starting piece. Don’t worry! You can fix it:

6. Add a Loop cut aligned to the starting piece’s edge.

7. Go to the Wireframe view and delete the interior face hidden below the starting piece.
8. Select the first couple of vertices you want to merge, press M on your keyboard, and select “At the center” in the Merge Menu.

Note: Once you have done an operation, it’s unnecessary to remake all the processes again because Blender has a memory called Repeat Function. Instead, select the other vertices you want to merge and press Shift + R to access this new function.

You can add as many details as you want in your 3D indoor space, like stairs or different types of doors, knobs, or windows. Anyway, it's your world. The possibilities are endless!