wall reinforcements and a temporay roofing are installed in the second stage load bearing walls are erected and fixed to the initial vertical wall reinforcements with mortar keys that fill indentations in the precast elements complimentary wall reinforcements are poured and lintels doors and windows are installed in the third stage the temporary roofing is relocated at a second extension while in the first extension a permanent slab is built and the interior partitions and finishes are installed the vertical wall reinforcements are cast concrete members of rectangular cross section have internal longitudinal and transverse reinforcing bars and are formed with a plurality of indentations of trapezoidal rectangular semi circular or triangular cross section shape cast in the outer surface application_number US 83929292 A description the improved building system for the progressive extension of dwellings consists of a series of stages and components to be described in full as follows fig1 and 2 are a comparison of what can be accomplished with a given investment during a first stage of construction using the system of the present invention as shown by fig1 and what could be achieved with the same amount invested and the traditional system as shown by fig2 as can be seen given a previous construction 1 and a minimum investment the system of the present invention would produce a light and reusable roofing 2 providing immediate benefits to the user while using the previous technique would only produce the foundations the owner then would have to.