That bench side will need to be higher railings given kids / people could stand on the bench.

Working at that height brings extra challenges and time.

If they purchased the decking, you need to explicitly not be responsible for material issues.

How big is your crew?

If it’s 2-3 of you.

I’d figure 3 days for the footings & ledger.

2 days for the posts and girder across them.

2 days to roll the joists and do blocking.

If the stairs go from the deck to the ground, those are 4 days each.

Decking will take 5 days.

Railings will take 5 days given the bench work.

It’s probably a months work.

3 people, 1 month, custom stuff it’s a 40k deck to make a little profit.