The opportunity to carry out a rehabilitation project of a flat on the top floor of a building from the mid-30s, led us to the challenge of building a roof-house. The fact that our clients acquired Matheiu and Lucy , a Franco-British couple who chose our country to live with their two children, own the exclusive use of the adjacent terraces and cover, led us to think about the possibility of creating a living space and contemplation on the roof, thus benefiting from breathtaking views, both to South and Castle, Pombaline and Tagus river; as to the North, to the Eduardo VII Park. Following the concept developed in the Asian continent, mainly in Japan, with notable examples of architecture where the cover is considered as a new frontier to be explored architectonically and an opportunity for the enlargement of the inhabited space through light and autonomous structures, we thought of a hybrid construction and totally independent of the existing architectural lexicon, having as a reference the concept of "TreeHouse". The wood emerged naturally as the material that best suited the project's intentions, both for its technical characteristics and for the characteristics we wanted to show, of a construction reversible and ecological. The construction is implanted in the terrace of the cover of autonomous way looking for its own space and establishing levels of spatial hierarchy in the remaining space, promoting it and classifying it.