First of all - do a lot of surfing on the web for other amateur observatory sites. I looked at pictures of their installations and read their logs if they were available. There are a number of people around the world who have done this before and most seem very willing to help out.
Use the vendor's knowledge. I must have driven my vendors CRAZY with my endless questions...but it is a lot of money to spend without some planning and guidance.
Decide what it is you want out of your observatory. Is it just someplace to just get out of the cold or a slightly smaller version of Keck? Remember that if you plan your building up front carefully, you can turn a shed into a very nice observatory over time and spread the cost.
Set your budget. I can tell you that the $$$$ went flying when I added this and that to my orders (Gee, did I really need a color wheel if I have never done CCD before?). If you are not careful, you can add many thousands to the cost of your observatory and not realize it until the end.
I am compiling a complete vendor list now - but here is an overview:
TECHNICAL INNOVATIONS (My guides and gurus) http://www.homedome.com
Pocono Mountain Optics (No web site)
Astronomics www.astronomics.com
ORION http://www.telescope.com
CELESTRON http://www.celestron.com
Le Sueur Manufacturing Company, Inc. http://www.astropier.com
Garden Solutions http://www.gardensolution.com
SkyMap Pro6 by Chris Marriott
TheSky by Software Bisque http://www.bisque.com/
The reason is the additional cost of the 10' dome. I really agonized over this for quite awhile. In the end, I decided to construct a building that can take a 10' dome in the future and start with a 6' dome. This left me with about $2500 extra in my budget to buy my CCD system
ahem, it's me. I leave it to your imagination why this is my nickname...hey! That's not the reason!!!
Hey! How did you know I live in the Northwest?!? Oh, the latitude and longitude on the home page....
Well you're right! it rains and rains and rains....but when it is clear ....it is BEAUTIFUL!
If weather permits, the first week in June. I plan to have a party and I will take pictures...maybe blackmail will help me pay for this endeavor!!!