I was planning an art-deco bookcase for the back room (see here), but reality has rather intruded.  We did a massive cleanse (for us at least), and threw out or gave away over 500.  But, when we did the maths that still left far more than would go into one walls-worth of bookcases, even if they went to the roof.  Building two was going to be wildly expensive and time consuming, so we decided to go back to a simple model, though still roof-high and with doors on to keep the dust out (photo below shows both bookcases side by side, though they are on opposite walls) :-

After quite a bit of research, the best option appeared to be the venerable Billy bookcase from Ikea – with vertical extensions it goes over 9 feet up.  But, the old design lives on – I plan to bring it out at some other time.