Hi Griffo, welcome.
I notice you're from Swansea - not far from Ed (Orion)?
Are you coming to
IISAC2007?
I bought my EQ platform from
www.roundtableplatforms.com, and i've been very happy with it. I've had it for about 18 months. Petra (spacezebra) bought one more recently too, and I believe she's also happy with it.
Others on the forum have the skills and ability to make their own - they might help out with plans etc, but I just didn't have the skills, tools or the time to consider making my own.
I'll be selling my EQ platform within the next month, so if you're interested, keep an eye out. I use it with a 10" GSO dob. I'm not sure how big the base for the 12" is - if yuo give me measurements i'll check the size of the platform.