Hey Brendan,
I too have being looking for plans, but, grasshoper, there is much to learn before we tackle the Dragon.
Mate, plans forget it. You should have an idea of what you want, how big is practical, and larger or largest aint necessarily the best.
I've built a 10" dob (comercial optics), following this book: "Making and enjoying telescopes" Robert Miller & Kenneth Wilson. It's ok for the smaller diy project. Hey, it served me well. You can get a 2nd hand copy through internet book stores very cheaply.
My next project is considerably larger. Really, there is no getting past the 'holy grail' of scope manuals: "The dobsonian telescope; a practical manual for building large aperture telescopes" David Kriege & Richard Berry.
I had tried to skirt around it, but in the end, those who know more than us won out, so I got a copy.
What it describes is indipencible for properly understanding why and how dobs work.
Once you work out what size would work for you, look up that range of aperture in your prefered search engine, and use what you find to hybridize the design a little further.
I'm hoping to get stuck into a 17.5" puppy soon, however, I'm carefully planing its DNA, to achieve a workable design for me.
Hope I've helped. Don't rush it. Don't be shy to ask. This mob knows no fear or shame,
!
Here's another suggestion, I'll be at the Randwick Girls' High astro night next Friday, follow the 'International year of astronomy' forum thread 'Sydney Astronomers'. I'll be there with my 10" scope. There will also be another ripper scope achiveable with the 'holy grail' book, Coooool.