I just finished building a prototype (cheap materials) of this pack before I make the real thing and it turned out great. This is a great design and the community that Stephen Jones of Bag Buff created on Facebook is a great resource for answering questions related to materials and the build itself. I highly recommend this pattern as a way to cut your teeth on pack making.
Ironed the pattern flat on low heat, cut out the template, signed up to Bag Buff for additional input. Bingo! I actually made a backpack! Very pleased.