Storage room vs stair cupboard - is it useful or just hype?

I will try to build it myself, however, I have a spiral staircase and for me, it will be more of a Harry Potter chamber. So with a timber frame and drywall partitions and then shelves inside, etc.

I just wrote a nice long answer about what the wardrobe should provide and then deleted it..

Unfortunately, I can no longer quote where there is a smiley :( 7000 would be too much for me as well, but we don’t know your stair situation either. Basically, you need the storage space, so why not simply have a door at the highest point and then a coat cupboard under the stairs. I have it similarly: https://www.hausbau-forum.de/threads/schuhe-und-jacken-auf-1-37qm-realistisch.38783/ That was a very inexpensive thing ;)

Our offer amounts to €6900 without painting, which my brother-in-law (master painter) will do

Is there also a plan for it (dimensions…) and a list of the interior, the pull-outs, etc.?
It makes a difference whether it is 2.5 or 5 m long.

We also had a "slanted cabinet" made for sleeping/dressing, which I still regret today. I should have raised the knee wall; then you could have used an off-the-shelf cabinet.

The cabinet cost €3300 including installation at the furniture store in 2013 (custom-made). 3.3 m long, height 1.7…2.6 m. Painted fronts.

Is there also a plan (dimensions…) and a list of the interior, the pull-outs, etc.?
It makes a difference whether it is 2.5 or 5 meters long.

I had already had the staircase cupboard in mind for a long time and then unfortunately forgot about it because of all the other side projects I currently have. So I was offered to create an offer based on the picture, so that I at least have an approximate price and can make a decision.

"Dear Mrs. XXX; the offer for a staircase cupboard like in your example picture would look as follows in your case: execution in 19mm white particle board including material, measurement, manufacturing and installation, including 19% VAT approx. €6900,-"

I don’t think we will be happier if we do the staircase cupboard. My husband was not 100% behind it either, so it remains the closed storage room under the stairs!