Yes, it must be "a house with 3 rooms". It's the common way to describe a house in the countryside, the most appropriate translation should be 3-room house.
Individuals can build houses belong to rural self-built house from the perspective of government management,the most common are tile-roofed houses and bungalows before 2000 in my hometown, if there is no additional explanation generally only one floor.
By the way, for rich families, may build small western-style houses which always have more than one floor, people never describe these type of houses whith number of rooms (almost every family can build a multi-foor and more beautiful house after 2010 in my hometown).
For a tile-roofed house or bungalow, the only modifier can be used is the number of rooms because these type of houses mainly to provide the function of living which have no extra decoration also no commercial value. And you may see descriptions like follows in articles and novels about rural life:
- 他那么努力做工是为了赶在结婚前盖三间瓦房("He worked hard to build a 3-room tile-roofed house before got married.")。
- 老房子已经破到没法住了，他用仅有的积蓄盖了两间平房("The old house was too dilapidated to live in, he built a two-room bungalow with what little savings he had.")
tile-roofed house: 农村瓦房
slabstone-roofed house: 农村石板房
And I have read your link to Hinative, the people answered your question seems have never seen tile-roofed houses and bungalows maybe they are living in cities and never heard or seen these type of houses so can not get your point. Tile-roofed houses and bungalows only occured in rural area, with the development of the economy, there are few now.
And I happened to go through this process, although I live in the city now, but my hometown is in the countryside, I used to live in slabstone-roofed house, tile-roofed house, also seen neighbors' bungalows when I was child.