Reveal Object Progressively

Hello,

How do you make an animation of an object growing or progressively reveal the object?

Here's an example of what I want to do, but I used a huge plane to block out everything else then moved that along the lofted object. Is there a better way to do this and a way so that you don't need to use planes, which block everything else out in the scene.

I can do it fine if the object is say a standard primative - ie. box - by animating and increasing the segments as I want, but how to do this with complex objects like lofted objects, curves and poly's?

Hopefully it's clear what I'm trying to do. Sorry if it isn't.

Also, can anyone recommend any good tutorials, preferably video, on making construction videos or good examples, that show how the architecture/building/object is put together piece by piece. Something like this:

Thanks

My first thought would be to use Fog, or maybe a particle system, but I'm not really sure. That's just a guess. I don't do much animation.