Today, I designed a parametric model of an architectural house. All the components (Exterior wall, interior walls, slab and roof) of this house depend on only one parameter, i.e. the length of the exterior wall. Certain expressions are used to set the dependent constraints. Refer this link for further readings: (https://www.freecadweb.org/wiki/Expressions)
The FreeCAD file of this model can be downloaded from this link: TestHouse
Feel free to test and review this parametric model.