Just wondering if you guys could point me at something that would give me a clue as to what is involved in building a press (prints, drawings, whatever) and a rough approximation of what it would cost to build one. I'd like to have one for pattern welding, as my hammer arm is getting along in years, or more accurately, I am sick of trying to find a striker who can actually hit straight.

The best resourse is James Batson's "How to Build a Hydraulic Forging Press". You can buy it through the bladesmith quild website and other places.

I second Randy's suggestion..it is the best booklet out there for such things.
I have had three presses (sold one kept two) and am working on a fourth....they are good tools, but it is best to build them well as they can do some odd things if they fail under load.
In general I would say once you have 20 ton or so go for speed over tonnage....30 ton at one inch per second will do more work for you than 100 ton moving like molasses.....I would caution not to go faster than two inches per second...and keep all tooling short and hands/head well away.
Keep the lines covered as when they fail it can forces fluid into your skin and this is not good...a thin sheet metal cover is all that is needed.

There will come a point when you are perfectly comfortable working with the press...that is when you need to pay attention.

Ric