"Hytta" is a feminine word, and if I'm not entirely wrong, all feminine words can also be masculine. "Hytta" could therefore also be written "hytten" - means the same thing, however, I personally think "hytta" sounds better (might be a dialect thing). Same thing with "flua/fluen" - the fly, "stua/stuen" - the living room, "lampa/lampen" - the lamp. The first word is the feminine version of the word, which would have the indefinite article "ei" and the last word is the masculine word, which would have the indefinite article "en".
Both of the words in the examples above are equally right, however, I think the feminine version is more dialect and the masculine.
Hope this helped more than it confused you...