There's a word which is specifically about building construction in progress - "долгострой".
When finishing some building project - building, bridge or road takes more and more time and still far from being finished - it's exactly
Quite often it's used not only about building. It can be used for describing state of software development (like here - "Долгострой в разработке ПО: о проблемах управления требованиями") or some political reforms - than it's "политический долгострой".
Still, this term is not universal. The closest you can get is
затянувшаяся работа or
незапланированно долго затянувшаяся работа.