Hey Rosy. If you've read all this lot then you're probably feeling a bit deflated by now! If you've only just managed to talk Hubby into a small hen house, then he's not going to necessarily take the idea of a new shed very well, is he?!
I would have loved a shed for the girls but it just wasn't practical in our small garden. We already have one shed, as do most people, and loads of kids toys... A new shed, however small, just took up too much space. It must be useful, having something big enough to get inside and clean, but it wasn't for us...
Have you considered the next size up from the one you are looking at? We have a similar one but bought two runs exactly like that in the picture (we put one in front of the other, hooked them together and took the door off the "inside" one). The girls are only in it when we're doing something like mowing the lawn or when there are half a dozen toddlers tearing around, the rest of the time, they free range the garden. Having said that, I am thinking about keeping them in the run in the mornings so they eat more crumbs and not shoot out of the run and scratching about. Mine are ex-batts so they need to bulk up a bit on proper nutrition!
I think the space issue is more about the daytime space (i.e. the run) than the bedtime space (i.e. the house). As long as there is a nestbox in the house and there is plenty of perch space then I don't think house size is so much of an issue. If the house has a removable floor, like ours does, then all you need to do is turn the house on it's side and - bingo - all the access you need.
Oh, and the next house size up has no windows, like ours, so they'll be quiet (ish) on summer mornings.
Don't be put off, you just need a bit of a re-think, based on what is practical for you but also adequate for the girls.