I have a Miller 252. It's done great service for me over several years, generally delivering welds which are often better than I deserve.
Here's the build thread from Pirate where I took up fabrication seriously. It's extensive and picture heavy. If you scan through it, you'll see that I don't have a huge amount of experience, but I'm good at learning.
I have no experience with doing internal cages, so just like last build, I've been reading. Generally the plan for this build (unlike the last) will be to use a lot of kit parts, including a cage kit by Redline from CO.
To assemble the cage, I gather that there will be some fitting and tacking to do with the cage initially positioned, then the floor gets cut to drop the cage down from the ceiling. After welding up all the joints, the cage gets raised back up and the floor gets plated.
I've heard stories about that knee action and other strange gyrations. I've also heard mention of hand actuated torch controls, funky bendable torch bodies, shortie back caps, gas lenses, and various gymnastic tricks for dealing with tight spots. I've yet to deal with any of this.
Frankly, until you just brought it up, I'd conveniently forgot about all that stuff...
Ignorance is bliss, but it can also be expensive.