Shelf for attic - sloping roof without knee wall

Yes, but that's exactly the point. Something like that is totally overkill for a warehouse.

If you already have sloping ceilings upstairs or need it under the stairs. OK.
But in the attic, I think the money is way too precious. Unless you can do it yourself, but even then – just the material alone!

Heavy-duty shelves are really unbeatable. I thought it over again. Even compared to shelf boards directly attached to the beams with brackets or wooden slats, at 5 EUR per board, you have to manage that first; with a shelf board, brackets (or slats), and screws, you're quickly at 10 EUR per board.

And then it's not even clear if you are allowed to load the beams that heavily...

The question is also whether you really need the space all the way to the full depth. We only covered about 20 sqm with floorboards in the middle, and even that is so much space, we don't need it by far.

When I look at the boxes that are still stacked up to the ceiling in our hallway and at the third children's room, which is filled with [Werkzeug und.... Zeug]... as well as the utility room, which is full of laundry bags, and then also the basement part that I still have outside, we would probably need 30 m2 of storage space with high shelves if we wanted it to be clear and accessible. Of course, we could also sort out and dispose of at least half, but I just can't convince my wife of that convincingly enough.... Although, the [Werkzeug und Zeug] is mine. But we still need it for the house, obviously... ;)

You don't want to store tools on the floor, do you?

Yes, but that's exactly it. Something like that is totally overkill for a storage room.

Yes, that might be true.
In my case, the attic is converted and serves as a guest room; that's when I dealt with the view.
And in my case, there is maybe 50cm of standing room width in the middle; if I put a "normal" half-height shelf there, I can almost no longer walk.
That's also how I understood it from the OP:

I simply have the "little problem" that my attic isn’t very deep either. Meaning, if I place a shelf too far forward, it quickly comes at the expense of walking space.

You can see here: the sliding door at the back is by no means 2m high but more like 1.70m...

You don't want to store tools on the floor, do you?

Well, yes, everything that is not electric, anyway. Or later in the garden shed.