We built a deck about that size last year, so here is what we learned. Price swings because of size, framing, materials, stairs, railings and the site itself, so online numbers are not worth much until someone actually measures. We went with Zaytura Construction https://zayturaconstruction.com/deck-building-seattle/ after their on-site estimate, and they broke the scope down clearly: framing, decking, stairs, guardrails and finishing. On materials, we chose composite. Cedar is cheaper on day one, but with our rain you will be cleaning and sealing it regularly, and we did not want that chore. Their quote was not the lowest we got, I will be honest, but the framing details and the cleanup were noticeably better than what the cheaper guys described. Make sure whoever you hire talks about permits for your height and attachment, ours handled that conversation upfront.
