Trending to green and sustainable buildings became inevitable during the increasing crises of global current lack of resources and energy besides all forms of pollution. Architects play an important role in reducing the environmental impact of their buildings through a good understanding of the negative impact of construction process during full life cycle and how to reduce it. Selecting materials and products for a high performance building is not an easy task as there are a lot of considerations and criteria for comparing the available options. This paper focuses on Life Cycle Assessment (LCA) as a method to evaluate the environmental impact related to building materials at different stages and how to assess and compare it with alternatives based on its environmental efficiency. The paper also includes a practical study conducted by the researcher using LCA tool to assess and compare two optional designs of two residential buildings with different structure systems, reinforced concrete and load bearing walls, depending on their environmental impact to prove that applying LCA in early design phase can make a difference in building design and the selection of building materials.