Thread: suspended slab roof versus truss and tile COSTS

Hi Guys,
I'm about to go through the motions of attaching a double garage 6m x 6m off the front of my house and the intended style/material was to be timber frame/blueboard and rendered and a tile roof hipped and one end and gabled at the other and grafted to the front of the house but excavated lower than the house as i'm on the high side of the block. just in the planning and costing stage at this point.one dilema i have is that the pitch of the roof 15deg min will cut the corner off the front window at the height im dropping the garage still and though i can easilk replace the window for a shallower one i was wondering if anyone has had any experience and cost comparisons between truss/tile/guttering versus constructig the garage with a flat suspende slab roof that would take the place of the verandah that has to be dramatically cut back to allow for the original plan? obviously being a slab id have to go with brick or block walls and steel lintels etc for openings but how much more would t cost to go this way rather than the conventional construction and materials? anyone had this situation before to consider?? ps....if it were to have a flat concrete roof/verandah where does the water runoff go? ie...drains in slab or guttering still?
pps......thanks for no help wollongong city council
Cheers
Jagfromaus