Learn Hardcore German: Wegen der Baustelle bauen wir provisorisch eine kleine Brücke. - Because of the construction site we are building a small temporary bridge.

In standard German, the preposition wegen governs the genitive case. Baustelle is feminine, and the feminine singular genitive article is der. So wegen der Baustelle = “because of the construction site.”

But der Baustelle could also be dative, right—so which case is it here?

Formally it’s the genitive. It looks identical to the dative because feminine singular genitive and dative both use der. You can see the difference with masculine/neuter nouns:

Genitive: wegen des Regens (because of the rain)
Colloquial dative: wegen dem Regen

Is it acceptable to use the dative after wegen in everyday speech?

Yes, many native speakers say dative (wegen dem Wetter). It’s very common in conversation and in some regions (e.g., parts of southern Germany, Austria, Switzerland). For careful or formal writing, prefer the genitive: wegen des Wetters. In your sentence, the form doesn’t change because it’s feminine.

Why is the verb before the subject (bauen wir) after the initial phrase?

German main clauses are “verb-second” (V2). If you put a phrase first (Wegen der Baustelle), the finite verb must occupy position 2, so the subject follows it: … bauen wir …. Without fronting, you can say: Wir bauen provisorisch eine kleine Brücke (wegen der Baustelle).