I have many a client drop into my office with vague ideas about what they want. I suggest beginning with a "wish list" and then proceed to clip images from magazines and the internet that catch your eye. This gathering process will help you to focus your attention and definitely help me to underderstand your thought process for the design. The images don't have to be exactly what you are after but close and relative to the detail and outcome you desire. I suggest you start a scrap book. The next stage is to define the room sizes and this can be easily done by measuring your existing residence and comparing sizes with future needs.

 If you don't use a house designer to create a custom home and believe there is a plan out there for you, may I suggest you browse through the catalog from the COOL Houseplans Company. 

home plans by The COOL house plans company