[Zeke]

A lot of the time the first number you see is a lump sum. That's a qualifying number to see if you are in the game. When it comes down to selecting the bid you like, the numbers can come out. If a couple of competing contractors won't break it down somewhat, they aren't really all that interested.

Your project with the roof load for a garden and the waterproofing needed is a very involved deal. Odds are that no one you can find has ever done this, therefore no baseline.

Using a very professional contracting firm can prove to be expensive. It takes a lot of hours and people to create a line item proposal. To pay for all that they have a significant mark up.

Be patient. Let them come to you after the initial contact. And consider hiring some of the work directly. Let's say you hire the masonry out to an independent and then the framing work.
Chances are that things will start to fall in place. One thing, you will have control over each aspect.