Buying a DH frame to build an Enduro?
If you are doing this to get a better Enduro and a Better DH bike, I believe this is a really bad idea.  If you are doing it because its fun and you want to play and learn about bike building, dive on in, but be prepared fro less than stunning results at higher than expected prices.   

Given the manufacturers are fully aware most people have an S ( refer  Rule 12 ) of 2 or 3, they spend a lot of time producing a wide range of bikes that in their range, there is one that will as close to a perfect  compromise of price/performance/style for everyone. Unless you are a very skilled rider, and a skilled bike builder (not assembler) I believe it's bordering on arrogant to think you can do better cheaper.

The other issue is the bike components them selves.  Would you rather have a $500 enduro fork and a $500 Down hill fork, or a single $1000 fork. My money is the single $1000 fork will do both jobs better. Same applies to wheels, gear sets.....  

If you have done all that, and still feel the bike is the limit factor of your riding, you probably need two bikes.