New Building Information Modelling (BIM)enabled performance metrics are gaining importance in Building Performance Simulation (BPS). However, scarce work was published featuring holistic metrics for prototypical designs in hot arid climate. Thus, this research presents a BIM-enabled sustainable early-design decision support tool, whose optimization variables are building orientation and Window-to-Wall Ratio (WWR). The mode's objective is reaching optimum building Sustainability Combined Score (SCS); the holistic value of performance parameters considered by the user. To demonstrate the methodology, the daylighting and thermal comfort metrics are considered: (1) Day-Lit Area (DLA); (2) Daylight Autonomy (DA); (3) Mean Daylight Factor (µDF); (4) Useful Daylight Index (UDI); (5) Temperature Discomfort Hours (TDH); and (6) Humidity Discomfort Hours (HDH). BIM simulation is carried out for various combinations of building orientations and WWR, metrics are converted into percentages then into criteria scores based upon expert-determined criteria rating scales. Next, using the Analytical Hierarchy Process (AHP), Criteria Relative Weights (CRW's) are determined, using a Pairwise Comparison Matrix (PCM). SCS's are computed for each scenario, as a function of criteria scores and CRW's. The verification of the AHP Module is done arithmetically using consistency indices. After screening all valid scenarios considering site constraints, accessibility and design codes, the scenario with optimum SCS is obtained. Three cases of prototypical designs, comprising a school building, a civil defense facility and a congregational building are presented. All cases are located in the hot desert climate of Qatar. The validation of the SCS Module output is carried out using expert survey.