My best advice is to let someone else build it, so if it breaks again it's on their dime.
There are a lot of things that may have caused it. Not breaking in your cam right is probably the reason. You should rev it to 2000+ RPM for 20 minutes. If your heads have dual springs, you should take out the inner springs to reduce some tension.
You need to use the right
oil as well, like Valvoline racing
oil and a bottle of Comp Cams Break In lube.
Good luck with the next one,
Joe