If your home improvement project is relatively simple a builder with experience in that type of work may be enough to provide advice, draw up simple plans and provide an estimate.
Architectural consultants and designers
If the renovations are going to be more complex - with additions to your property for instance - then speaking to an architectural consultant or designer may be a good idea. Draw up a brief and wish-list of requirements, and think about your budget before you contact them.
Many architectural designers or consultants offer a one-off consultation that provides guidance about design and construction. You can also instruct them to obtain the necessary building control and planning approvals, (although you will always be responsible for complying with them).
Although there is a cost associated with hiring one of these professionals they may well be able to advise you on ways to keep costs down, both during the build and on future energy costs - with sustainable design.
Another professional you or your architect may need to consult is a structural engineer.
This will be the case if you make any structural changes to your home or if you're adding a new structure.
So if your project is taking down a chimney or a load-bearing wall, building an extension or carrying out another piece of major structural work, your architect or building control surveyor may advise you to employ this particular type of professional.
For a more complex job like a large house extension you might like to employ a project manager - an experienced one can potentially save you time, money and stress.
Or if you're organised, decisive and quick to learn you may be able to project manage the project yourself - but do extensive research and planning before you take this job on.