Cost indices are considered as important tools which help both the owner and the contractor to identify the primary evaluation of project depending on the cost of previous and similar project in easy and quick form, and the most important using ways by researchers in process modernization previous cost in shortest time and least effort. Methodology was adopted to help in designing cost index taking into account weights of chosen groups instead of weights of items, so It has been suggested three cost indices for school building in Lattakia by studying a sample consists of 32 schools were constructed between 2001-2012, and then The best cost index between them which explains the biggest portion of square meter cost variations due to escalation was selected, also it has been suggested a model that reflect the relationship between cost of square meter and developed cost index for corresponding year through statically program spss.