A method for making a deep draft semi-submersible drilling/production vessel having a center of gravity below its center of buoyancy by constructing a plurality of buoyant individual columns. The method connects a pair of columns with at least a first top truss and a first bottom truss. The method additionally floats a connected first and second columns horizontally in water. The method floats the semi-submersible structure to a location for installation. The method concludes by deballasting the semi-submersible structure with connected deck forming a semi submersible drilling/production vessel having a center of gravity below its center of buoyancy with a draft between 300 and 500 feet.