Probably you're asking about the ratio of costs of building a bike, but your question is ringing differently in everyone's ears -- mine included.

My first reaction is why you'd build a bike using all new components on a budget of $1,500, but maybe that number is just a placeholder. Anyway, I agree with everyone who said you'd get a lot more value buying it already assembled.

Generally, building up a new bike, I'd say you'd spend something like 2:1:1 on frame: wheels: components, but that pretty loose.

If I were to build up a $1,500 bike, and you'll allow me to use non-new parts, here's how I'd attack it:

frameset: 300 for used Trek carbon or something similar
wheels: 500 for Zipps or similar
saddle, seatpost, bars, stem, etc: 200 good saddle, carbon seatpost, alloy
group: 500 for 10-speed

Here's where I think spending more money than the cheaper option really helps, roughly in order:

1. Tires
2. Wheels
3. I'm not sure what to put next

And here's where I'd save money:
1. Handlebars, stem
2. Frame