GregArchitects play an important, essential role within the construction. They aren’t typically speaking involved in the day to day management of a construction site and building project, which is what a construction manager will be doing, but will instead play an important role in the planning and design of the building. Once the project has begun, architects will, more usually than not, only consult at certain points of the project to see that nothing unexpected has happened.
Knowing all this should give you some idea of when you need an architect. Basically, whenever you’re building a new structure, an architect can be immensely helpful in ensuring that you use every opportunity available to you. If you’re carrying out maintenance work, there isn’t usually a very good reason to consult an architect; a building surveyor and construction manager are far more suitable (although only once the project has reached a certain scale).
A lot of people go into a building project with an idea of how they want the building to look once complete, but the vast majority of people don’t really understand what accomplishing all of that involves. An architect will be well versed in the physical capabilities of certain construction methods and materials; knowledge that will be essential for determining whether or not an idea is possible or not.