The vast majority of self-builders have never built a house before, so undertaking their first self-build project is a huge challenge. Many have also never worked with an architect before, so they do not know what services an architect can provide.
In brief, an architect's role is to understand your requirements and then visualise your dreams and aspirations.
It's important to note that architectural services can theoretically be provided by anyone, but only those on the ARB Register of Architects can use the title of 'architect'. An architect has had over 7 years of training (minimum) in all areas of design and construction so that they can provide a service on whatever design challenge is put in front of them. The architect will take your initial project brief (ideas, requirements and budget) and the site information, then will come up with various design options for your consideration.