Originally Posted by mkc

I would recommend looking at some home dec workroom sites for idea. That large a worktable is more along the lines of their setups. Try workroomtech.com and look at some of their articles, like this one

Be aware, without support (similar to having floor joists), if there is too much gap spanned between the bookcases the plywood will sag and bounce. It is not a rigid item, especially with a long, unsupported span. You need to fabricate something to support the plywood.