I have a pretty extreme view on this – the last couple of site designs I have been involved in I have (a) asked customers (b) pulled together some best practice from other people (c) applied some logic and commercial judgement. Finally you need to build in as much flexibility as possible – you don’t want to be reliant on developers for changes all the time!
The more you give a designer to work with, the less chance there is of endless tweaks which will eat into your budget.
Design is important but it shouldn’t have to break the bank. When you’re next engaging with a design firm, make sure they give you a fixed price for the work and ensure that you get a number of options to choose from with a number of amendment stages. At Pod1 we don’t stop until we get it right and the client loves the work, but we do charge a premium for the service. I guess you get what you pay for.