As a solo freelancer, in order to take on larger projects, you will need to build a trusted team you can work with.

This will take time and effort.

One way to begin, is by joining and participating in local user groups, attend the workshops and social evenings. You will get to know other freelancers, what their strengths/weaknesses are.

Assume that if you are going after larger-scale contracts, you are also taking on some responsibilities, including

Account Management / Project Management

Requirements Analysis

Quoting and setting Payment Milestones

Ensuring your clients are happy and your designer/developers are happy

Consider where it leaves you if either a) the client doesn't pay, or b) your freelancers don't deliver as promised? This going to happen from time to time - how will you handle it?

Going after large-scale projects is doable as a solo-freelancer - but make sure you know what you are getting into when you are assembling and managing project teams.

When it works - it's a dream - and can be very profitable.

When things go south - look out - it can be a world of pain.

I worked for a web firm first, managing large scale projects - that gave me the experience to do it on my own.

If you don't have that experience, then be frank with with the freelance team you put together about your goals and ambitions - make sure they are the type of people you can rely on - and that they are willing to work with you to go after the 'big fish.'

It can be done! (But it's not without its risks).