It's one of Trimaran Project and Multihull News blogs intentions to share knowledge and encourage more people into multihulls and this home built training multihull is one possible avenue. This boat is intended for a sailor of weight up to 60kgs (kids or a very light adult).
Chris Tucker has made available for free download and personal use the plans for a training catamaran the DS12. You can download the plans at the link below.
A gallery of the prototype DS12 catamaran under construction can be found here: