Is there a way to distinguish between "I build houses" and "I build (a) house"? Since no adjectives are present one cannot be 100% sure.
It it were just one house, it would have the indefinite article ett.
Is this rule valid all the time?
As far as I can imagine, yes.
Just to be sure: I doesn't work the same way as "Jag köper bil."?
Bra fråga, fast hus är ett ett-ord. Det heter ett hus - flera hus, men en bil - flera bilar.
Wouldn't it be "Jag köper bilar" or "Jag köper en bil"?
Is there no plural for houses? It's just house?
ett-words with only one syllable usually look the same in sigular and plural.