Please don't think I was in any way being negative, maybe a bit jealous though
It's just that most houses in Britain don't even have basements, let alone that kind of available 'utility' space due to the fact we're packed in tighter than sardines in a can (mostly).
I'm guessing with that many bikes and a small entrance (?) via stairs you'll want to keep your regular riders near the door? I find that top and tailing the bikes on one wheel from ceiling hooks is a great way to make the most of the space whilst keeping the bikes out of harms way. Like this, but on a grander scale