Insulating garage roof, correct sequence of execution

I have now had 3 craftsmen here to seal our garage roof. And I have now heard 3 different opinions and prices.

For a 6x6m garage, the price ranges between 1400 and 3800 euros.

But I only want a tight garage that does not mold inside.

What would be the proper method for sealing a garage roof?

Are 2 layers of bitumen sufficient?

Is a layer of insulation necessary in between?

Is a vapor barrier foil necessary in between?

How was it done at your place?

So the garage at the top should already be very tight - I don't think much of bitumen. I have EPDM foil there without a single seam - so one surface. Not cheap (material costs including adhesive are just over 1000 euros), but tight and above all you can immediately see any damage spots.

You don't need to do insulation underneath (so roof insulation), underneath you have to decide for yourself if you need it. I stuffed 200 mm wool between the rafters.

And you really have to install a vapor barrier, because especially now in summer you have incredible moisture rising into the insulation and thus the wood. I installed a climate membrane - simply because it masks smaller errors in the sealing. And it can't be completely airtight anyway, because for one I still have a gap between the clinker brick & concrete lintel of the gate (but there will be a cover plate here) and at the back the insulation goes directly to the clinker brick - is that airtight? Well, I can't present it differently.

I did the insulation & vapor barrier myself.

If I had a garage with a roof truss, I would probably do it the way you do, but I have a poured concrete ceiling.

I have seen this foil or a similar one on YouTube and suspect that this would be the best solution, but the price is quite high.

You can make it watertight with bitumen, I think, definitely, but inside it should not get wet because of condensation.

Inside it will get wet - unless you provide forced ventilation.

If the garage is not heated and well sealed, I don't see why it should become wet inside from condensation...?!?!? Sure, if you drive in with a soaking wet car at 35 degrees in summer, it will get a bit steamy in there, but so much that it eventually molds? Hmm...

It is cool inside, then you quickly get problems with condensation in summer.