It's not any harder or easier than a wood kit as it seems like no matter what you get you might have to fabricate some parts but just about everything need is off-the-shelf.
I built my Rampage following Marc's instructions and it turned out great so that's why I tried to use his on my Gen II. Insane's weren't any better, actually worse as I used theirs on my F-41 and they were a mile off. Sometimes you have to go with your gut feelings that something isn't right.