If you're going to build it, I figure one has the $$$. Get all three barrels. The 40 will work in the 10mm, but if I recall, I have seen 40 cal 1911 mags advertised, so there is a difference.
Don't download too much in the 10mm case. If there isn't enough power, there might be an accident.
If one is looking for 10mm brass, I've seen some on Gunbroker.com and ebang.com. Check under the user name: unique_reloader
I've bought some brass from this person, 100rnds for under 10 shipped. I could have spent 6 more to get new brass (16.00 @ my local shop).
I've heard that full power 10mm loads in the 1911 will have bad effects over time. Something about cracks forming iswhat I read before (might have been here too.) Pressures a 10mm operate at are much higher then the old war horse 45 ACP.