Elena wants  a house that can be built in several phases:
In 2015, a maset -small weekend cabin- to cook calçotades and costellades.
In 2020 a mas for her, Eduard and her two sons, that can also host friends and grandmother's visits.
In 2030, a house for each son might be added, and the grandmother might move to the ground floor. 
She needs to have a twenty year plan that can foresee the evolution of her habitat, and that at the same time allows the maximum possibilities:

She needs a plan that includes uncertainty and anticipation. The first phase should be as inexpensive as possible. It is just a tiny weekend hideout. It is also an outdoors classroom for her two kids, so they can experience and learn all nature's processes: