Hi, I am designing a concrete roof slab that span across 12m long and 9m width for my living area. The support columns are placed in each 4 corners and they are 300mm x 300mm size. The concrete slab roof is cantilevered out by 1.8m on 3 sides (not all 4 sides) with the thickness of 150mm. At the moment, the beams are connected to each corners with dimension of 150mm x 400mm thickness and height respectively. This living area is placed on the top floor of 3-storey house. The house itself is sitting on support columns alongated on the side slope of 35degrees angle (perpendicular to the slope). The top floor is on the hill top. the lowest floor is at the bottom of slope. Briefly about the surrounding. It is going to be built in non active seismic zone. there are lots of loose rocks/boulders. The entire hill is actually a granite. some of bedrocks are exposed. An average of 2m depth to the bedrock. Soil is sand/silt/clayey. There will be at least 30 pile caps on 8m grid. Questions, a) the idea of concrete roof slab is mainly for lounge decking. Might have some flower pots and a set of breakfast table. Do I still need to design the structure by taking into account the imposed load of 2.5kN/m2 to meet the requirement. b) Are my beams, columns configuration and size correct? How many secondary beams do I need? Do I need more columns? my idea is to build with conventional way with reinforced concrete beam and column with conventional rebars. c) is the column size good enough to support all the floors? does it need bigger size at the bottom? Considering they are supporting 2 floors above. Please advice.