Before starting the design phase learn the game rules (local building regulations).
When you want to improve your property, no matter if you are thinking of new build, remodel or refurbish an existing property:
You need to know what are the urban regulations applicable to your property.
Would you put illusion, time, effort and money into a design that will not be accepted by the local town hall architects and that might be rejected to obtain the compulsory building license?
This first step is a must for a successful architectural project.
Without being sure you have learned what building works are allowed in your property, please, do not start the design phase.