Just in case you don't know, most DNs these days have composite or Aluminum masts. If it's in your budget, a fiberglass/carbon mast would be a big improvement. I noticed one at a very good price recently posted here:
http://dnamerica.org/forum/index.php?topic=503.0If you decide to build a wood mast, there is a more detailed description on how to build the type of mast shown on the IDNIYRA plans at:
http://idniyra.org.hosting.domaindirect.com/articles/mast_made_easy.htmAs for wood, if you're not trying to build a super-flexible fiberglass/carbon reinforced wood mast, Poplar would probably work OK. Just be very careful selecting boards; my experience with Poplar is that the density varies quite a bit (and you want the lightest boards possible).