Title says it all really, "How to convert a vw bus or van to a camper". This is a decent guide to conversion for VW vans into a full blown camper van. It doesn't offer plans to build from but has good pictures and info which help to plan your project and method of build.
Build your own motorcaravan and the T5 conversion manual are both listed here too. These are both excellent reference manuals for modders and tinkerers.
Classic campervans 1956 to 1979 is positively the best present I received last year!