Buying a DH frame to build an Enduro? First of all, I haven't set my budget yet but I want to build a full suspension MTB in the near future.

I was thinking if it is a good idea to build an Enduro bike with a DH frame. I mean I know the suspension travel for DH is longer, so logically 'maybe' I can put an Enduro fork in there and effectively reducing the slack geometry (slightly) since the fork is slightly shorter (?), while setting/changing the rear suspension also shorter, also Enduro gearing, then boom I have an Enduro bike. Then when I want to do a more aggressive DH I can 'simply' change the fork and use longer suspension travel in the back and boom I have a DH machine.

Initially I was thinking this but with Enduro frame instead, but it seems more doable with a DH frame as 'logically' you can use shorter suspension on a supposedly long suspension frame than the other way around.

What do you think? is this a bad idea?
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.