Thanks Tom. This is the first one in my cabin, I have now four others including one in the house.
There are only three shelves supplied with these Billy Bookcases, the middle being part of the structure. I buy sheets of clear polcarbonate from a local DIY store, then using a normal long wood saw to cut out shelves (don't use what we call a small bladed hacksaw as the tiny teeth will jam the plastic as it gets too hot).
The internal sides are already drilled with holes, so I use sprue as pegs to support the shelves. I get with 1/24 or 1/25 scale cars, four across and two lengthways behind on each shelf. The second image is an old bathroom cabinet, again by IKEA, jusy slighlt smaller,