You're getting a lot of great advice already.
I'll just add in a couple things...
I'm also in the solid or plywood camp. Resist the MDF urge.
If you go with plywood, you can do 4 feet shelves if you add hardwood
facing.
These bookcases were done that way.
http://mikedrums.com/bookcases.jpg
The shelves are 3/4 ply with hardwood facing front and back. I probably
could have gotten away with just the front, but they have a lot of heavy
books and scrapbooks, so better safe than sorry. Plus, they're
reversible. :-)
Another advantage of the hardwood strips, is the look. You can put a
decorative profile on them if you choose. The added thickness, IMO,
gives the shelves better scale. These were rabbeted and glued.
--
-MIKE-
"Playing is not something I do at night, it's my function in life"
--Elvin Jones (1927-2004)
--
http://mikedrums.com
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