Which is correct "A huge unattractive block of flats" or "An unattractive huge block of flats". What is the word "huge" - an opinion or a size?
Google Books Ngram comes to the rescue, and suggests that the following phrases: "huge unattractive building" and a simpler version "ugly big building" are not recorded. On the other hand, big ugly building and huge ugly building are both cited.
This doesn't exclude the possibility of using the adjective unattractive to describe a block of flats or an apartment building (AmEng), it's just less common, and rarely used in conjunction with other adjectives.