If you are having a building project done then you may consider hiring a project manager. Some people think that having a project manager is just another cost that they can do without so take on the role themselves. A good project manager should have a lot to offer for any project and if taking on the job role yourself you will need to ensure you have plenty of free time to do it and have a good idea of what you need to do.
A project manager can often save you money on supplies etc. as they often have contacts within the industry that will offer them a discount. They are also there to keep an eye on your budget and on time scales, meaning your project is more likely t be completed on time and within the budget you originally set up. Before dismissing a project manager, find out the exact costs and see if it may be worth using one.