My Dad built a dollhouse for my sister that was similar to the plans BobA posted. It was very basic, but she had a great time with it for years. I think it each floor was about 18" high and there were three floors, plus a "deck" on the flat roof. This was tall enough that just about any doll or stuffed animal could fit inside, from Barbie to the Easter Bunny. Each floor was divided into two rooms by a partition that had a door hole jigsawed into the middle. I don't recall any actual doors, but that didn't seem to matter to my sister. There was also a hole in the roof so that the dolls could get onto the deck. Again, the lack of doors didn't seem to both my sister.
The crowning achievement, which I have to admit seemed pretty cool to me at the time, was an "elevator"! The right side of the house had door-sized openings cut in the outside wall. The "elevator" was a four-sided box attached to a string. The string ran through an eye hook in the roof. Pull the string and the elevator went up, let it go and the elevator went down. There were magnets at each floor that would latch onto bolts or steel dowels inserted into the elevator box and hold it in place; no need to tie-off the string. We didn't have rare earth magnets in those days, so the box was only big enough to hold one Barbie-sized doll.
I think construction was mostly done with 3/4" plywood, a circular saw, jigsaw, and a drill. The base was larger than the "house", to prevent it from tipping over. The back was screwed and glued to the sides. The roof was slightly larger than the house, it overhung the right side enough to support the "elevator". Floors were 3/4" plywood glued and screwed to the sides. Partition walls were inserted between the floors. They might just have been glued in place; I don't remember for sure. There were various windows jigsawed into the sides and back. Dad bought a few pints of latex paint in colors my sister picked out and then painted the inside and outside. Some plastic doll-sized chairs and kitchen appliances finished the project off. Despite the simple construction, the project was a huge hit with my sister...