Grega, the firm will fix the attic for you if you have 50+ thousand on the pile in a few months.
If you're doing it alone with just two hands from the lower parking..., the work goes a bit slower. Otherwise, don't know if you built anything yourself? Sometimes people can't even whitewash one room, let alone build from the foundations up.
Neighbor old-timer, who built two houses and cottage in his life, plus 40 years hard maintainer work on several buildings at once in Lj (Kolezija pool and bowling, G. Figovec, Slepi Janez...), told me: If you put the attic together yourself, well done, I believe!.