A room is a box with three, four or five sides depending on where in the dollhouse you want it. Each side is a rectangle, in addition we need interlocks. For my 4mm plywood I chose 4mmx10mm gaps. I did it the way that I have explained in this video (sorry English only as a subtitle) before: https://www.youtube.com/watch?v=FWwjCOHaWbU

Build all your sides this way.

If you want a door or a window, just add the required rectangles. For a window it looks nice, if you score a rectangle and then cut a smaller one. This way you have a “window frame”.

If you want many rooms, repeat this and glue the rooms together. If you have doors between the rooms make sure they are at the same position or just reuse the side.

Laser the sides and glue them together.

If you have a 3d printer: Look for free furniture models, you will find a lot of these. Print them and decorate your dollhouse.

But if you only have your laser you could construct furniture. Fortunately, most furniture is also rectangular, so made out of boxes. You can use the same interlocks here. I constructed a chair, a bench and a table. But many other parts of furniture are also simple to build.

Laser the furniture, glue it together. If you want to move the dollhouse later and ensure that everything stays in place, you could also glue the furniture to the dollhouse.