Best load distribution on beams from loaded slab can be achieved by defining the slab as a membrane without meshing (one way or two way slabs), take care when using non mesh membrane slab (two or one way) in complicated roofs, because Etabs will give the beams incorrect load distribution at some points and these points not always can be controlled. the results (in the attached etabs model) from the S300SHCON (where the material is normal concrete) is lower not higher than the other 2 types (note that the S300SH is the same as S300SHCON but using a different material to reduce the inertia of the slab section (by reducing the modulus of elasticity). Also note that all of them give higher results than the S300MEM2way which gives results similar to the manual calculations.