Build a new house or renovate, restorate an existing one?
Most people looking for a house ask themselves this question.
Each option has its advantages and drawbacks.

Build ex-novo

The main advantage consists in having a land. One has the freedom to build as desired.
Some limitations may come from the positioning of the house, access road and adjacent properties.
In order to match the clients needs within a budget, the architect may play with several factors: functionality, shape and dimensions, materials and energetical issues.

Renovate/restorate

we may distinguish between two types of approches:

a) renovation
b) restoration

More precisely:
a) A renovation is required whenever the client is not satisfied with the functionality of the building.
It must be very clear how far to go with the renovation. As a rule of thumb one should consider that the cost of the building plus the cost of the renovation should not be higher than building a new house.
One must start with the walls: modify the volumes, renew all the services (water, electriciy, heating), floor, finishings and paint. Very often the windows must be changed as well.
This process may lead to very convincing results as one tries to prize the existing structure while introducing new opportunities.

b) Restoration is usually reserved for buidings of strong architectonic interest, or more simply, to maintain a traditional aspect in a particular environment.
The job is more complex as the main goal is to higher the living standards (staticity, services, windows, floors, etc.) while respecting the historical characteristics and materials.
Matching theses requirements requires proficiency and sensibility.
It is an expensive but also very rewarding alternative.