DIY Spotlight?

I'm looking to find a DIY spotlight project that can be mounted to a roof and be seen for miles around. Anyone hear of a project like this? Looking at commercial spotlights are somewhat around 155,000 lumens. The cheapest thing I can think of would be to take 4 15 million candle power spot lights (the hand-held recharageable kind) and put them into a smooth drum of some sort to focus the beam.

I'm not really sure how to start on this one, any pointers would be helpful.
DIY idea

Look for a 1000 Watt MH lamp and ballast. I have seen them pretty cheap on eBay, or places like & venture lighting. These are used in parking lots and street lamps.

High pressure sodium is even cheaper to buy and run, but the light will have a funny color. (Maybe you don't care?)

On the other hand, either of these take some time to warm up and restart. If you need "instant on", then a halogen lamp would be better.

Then get a big parabolic reflector from Edmonds for $40 to $78:

Build a nice weather-proof housing with a small 120 VAC fan from Radio Shack, and you are in business. I would make the distance from the lamp to the reflector adjustable, so I could project a tight beam or a wider beam at will.