It's nearly impossible to be a "startup" in the construction industry. Aside from employment, permitting, funding, and real estate, the whole notion of a startup just does not work in the construction industry. The timeline is long and slow, the upfront commitment is high, and the entire endeavor is risky. It's not just writing code and creating a website.

Edit: There might be startups brought on as subsidiaries to do specific tasks, but I think those are very rare.