Approach

1. Listen to your brief. You will know what you want and how much you want to spend. You will have definite overarching requirements and may have specific ideas.
2. Make an assessment of the brief and the budget. This means checking that the budget is realistic and that the brief achieves your overarching requirements. For example; does splitting a house into two flats make it more valuable? Not if the cost to do it wipes out the profit. But maybe two flats are saleable when the house wasn't.
3. Research the facts. Find comparables to value the finished project. Contact my network of consultants, contractors and suppliers to confirm headline prices for cost of the works. Work out a basic programme of works to minimise disruption to the rest of the site or to realistically release portions of it for sale whilst works are on-going.
4. Discuss with you. You might find that the project doesn't make sense for you anymore or that there are smaller cheaper solutions than you expected. It's all fine with me – I am working to be your long-term advisor, not just for this one project. And if you don't go ahead, you will recommend me to others.
5. Firm up the details. This might mean cutting through local authority bureaucracy to get the critical questions answered or it might mean putting together a fixed price for the works.
6. Talk to you again. If it still makes sense for you, get contractual.  
7. Get on with it. I will keep you informed and ask you for any decisions with the time and information you need to make them.
8. Manage the project, representing you so that your requirements are met.
9. Represent you at every stage and in all negotiations – with contractors, with planners, with neighbours. Or not, as you see fit.
10. Make sure the paperwork is complete. This means; my architect's certificates, building regulations compliance, planning consent, CML or NHBC compliance, safety certificates, insurance company requirement compliance. The project isn't worth much to anyone else if you don't have these.