The natural convection is numerically investigated in a roof of triangular cross section under constant heat flux with seven different values depending on daylight on the inclined wall, constant wall temperature on the bottom wall and adiabatic on the vertical wall boundary conditions. Continuity, momentum and energy equations are solved by using finite volume method for laminar, two-dimensional and steady-state regime. Streamlines, isotherms, local and mean Nusselt numbers are presented for AR=0.25, 0.5, 0.75 and 1.0 and Ra=10(3), 10(4), 10(5), 10(6). The amount of heat flux ranges from 163 W/m(2) to 808 W/m(2) depending on daylight and the Prandtl number is chosen as 0.7. It is found out that the aspect ratio and Rayleigh number highly affect the heat transfer on the bottom and inclined walls while heat flux slightly affects.