Choosing the Kitchen
Earlier on in the design process your architectural designer will have given you some guidance on the kitchen design to ensure there is enough space for what you need including room for all appliances, that windows are correctly positioned and that the circulations spaces/doors are also well placed. Interior designers have a lot of experience in this field and can be really helpful in the early design stages.
But the most common way to design a kitchen is to visit a manufacturer and have them work through your requirements; they will usually put plans together for you on that basis. Most of the choices you make will be based on your tastes. Some may charge a fee for this service, refundable if you buy the kitchen from them.