I didn't use any books. I searched the Observatories forum here, and also a generic "personal observatory" search on the internet. That yielded all kinds of ideas about what to include in my building.
In my opinion the most important decision is how big to make the scope room. It's hard to make it bigger. Consider how many scopes you ultimately want set up and how much walking around room you'll need. If you're an imager you'll need less room than if you observe through an eye piece.
Warm room or no warm room?
How much storage do you need? In my case, I wish my observatory was 24" wider than it is now that I have two other scopes stored inside. Also, my observatory is remote and I didn't consider storage of grounds-keeping supplies or basic tools, so that had to be added.
Electrical considerations: your mount won't take much power at all, but dew control, cameras, focusers all add up. A computer also takes more than your mount will. You'll want at least some 120V power for miscellaneous stuff like a clock, a hair dryer (if you don't have 12 VDC dew control), perhaps a reading light for after you're done observing. Do you plan to have an air conditioner in your scope room? Will your roof (either dome or roll-off) be motorized? If you have a warm room, you may need quite a bit of power: air conditioner, lights, computers, microwave, coffee maker, TV and/or stereo. Don't laugh, I know a few people who have turned their observatories into full-blown man caves.
Actual construction really is last. Dome or roll-off (or roll away, or out-house or motel-o-scope)? Slab or pier-and-beam foundation? Stick built or prefab shed? Do-it-yourself or contracted? Permanent pier(s) or tripod(s)? If permanent pier, how will you construction the foundation for that? Roof from metal, fiberglass, shingles?
Good luck with your project. You will love having an observatory.