Buildin'
Well...I raely ever build one up starting with all new parts, but I think if was gonna go that route, I'd start with a Caspian frame and slide set. Get a Brownells catalog and start shoppin'. Whenever you have 2 identical parts from the same vendor, always opt for the more expensive of the two. Brown hardcore hammers come either cast or machined barstock, f'rinstance. The difference in price is small. Nowlin Pro-Match sears work well with that hammer, BTW. Sadly, Briley caved in to the "Cast is just as good" approach, and their excellent machined disconnects are no longer available, and I got the last three that Brownells had in stock, and no ya can't have'em.
The good news is that their cast disconnects are nicely done, though the one that I'm currently testing hasn't seen enough use to make a call on...yet.
EGW firing pin stop, fitted to a light press-fit and with a 5/64ths or smaller radius...EGW markets a very good checkered cast slidestop, but I don't care for the smallish locking tab. Brown Hardcore is also good, but no longer checkered. I like Smith & Alexander mainspring housings with lanyard loop.
A little cheaper without the loop. All are cast.
Colt sear springs, plunger assemblies, and Colt pins...available in the factory parts section. Wolff mainsprings and firing pin springs, and Wolff or ISMI recoil springs. ISMI lasts longer. Wolff is a little cheaper by the 10-pack. 16-18 pound range...and 14 if you plan on loading light stuff. Don't get sucked into the light mainspring crap, hoping for a better trigger. Stick with 21-23 pounds.