As you can't really buy them any more, I want to build my own shelving unit for my cassettes.

Ideally it would be one like this with individual slots for each cassette: https://img0.etsystatic.com/000/0/6762191/il_fullxfull.344023608.jpg

Alternatively, something like this where you can put the tapes side by side with a small gap at the top for ease of access: https://fbcdn-sphotos-a-a.akamaihd.net/hphotos-ak-xap1/v/t1.0-9/10376822_697229823676080_461697096836156905_n.jpg?oh=7b3d67a3e326f6974a4f14b3d462deb4&oe=54E80E2F&__gda__=1423908966_66fdb8ff51d40495a162ef5d049d3f5c

Never done anything like this before - are there any decent online guides for this kind of thing? I want to do something a little nicer than just nailing blocks of wood together.