Architects are qualified to deal with the complex problems involved in design and construction.
Insured to cover their services should anything go wrong
Will bring interesting ideas to the design of the house
Have the expertise required to plan houses that work efficiently, and are therefore more enjoyable to live in
Have the resources to do all the research, which needs to be done for your block of land and house construction.
If you ask, an architect will often be willing to organize all the construction needs including builders and trades people (the time taken to do this will be added to the architects bill)
Cons
Architects fees can be expensive and could blow out your budget. Some fees may be a percentage of the building costs, rather than a set amount. In this case, as the total costs rise, so do the architects fees.
You may not always see eye to eye on design issues.
Disagreement with your architect could cause you a lot of heartache. Architects tend to take ownership of their designs. This can lead to a bad experience if for example you want a colonial homestead and the architect envisages an Opera House on your block.
Things to keep in mind
See some of the projects an architect has designed and, if possible, talk to the architects clients to find out what the architect was like to work with.
Shop around to get an idea of the different architectural firms that are available for work in your area (eg. a sustainable practice/ a large firm).
Call the Architects Registration Board in your state to see if the firm is registered and what comments are available on their work.
Speak to the architect in person for some time. See if you get on and test your compatibility. This is most important as you may be spending a lot of time together!
Design 
