The built environment is and will be the place in which most of the people live and its expansion is unavoidable due to urbanization. However, such a phenomenon will increase further the already high material consumption in the building industry, as well as the waste generation. A development that rises many concerns in modern society and, thus, various solutions are investigated. One of the suggested solutions is the "living in a bottle" project from Ir. P. de Ruiter. The aim of this project is the use of computational design and additive manufacturing to produce mono-material building structures out of one recyclable material. PET GROWN is part of the above-mentioned project and investigates whether a self-sustaining, mono-material and multi-functional green roof system, 3d-printed out of rPET, is possible. The selection of a green roof module as a case study, is based on the green roof feature to reduce heat flow and UV radiation reaching the structure, two parameters in which PET is sensitive. With regards to the module, the study focuses on the replacements of the multiple material layers in a green roof, with one single material by using additive manufacturing. During research, design variants are developed, by using computational tools, and evaluated according to requirements related to functionality and 3d-printabiltiy. Then, the most suitable variants are selected and developed further to form the final project. The study highlights the influence of additive manufacturing in all its design steps, as well as, its advantages and limitations. In the end, the final outcome this study is a mono-material green roof design that fulfills most of the functional requirements of an extensive green roof.