Pitched roofs are preferable for snowy areas to prevent collapsing but flat roofs are great for rooftop gardens. Though I voted neither it really should be either or both because so much depends on the area and the need.

As others have said, it depends on your environment and view. If the house is located in a particularly hostile environment (e.g. west coast Tasmania, central Australian desert) or experiences wild swings between the seasons (e.g. Snowy Mountains) then windows are your friend. In temperate / sub tropical areas like Brisbane then verandahs are the way to go. Windows can have great thermal properties IF they're double glazed which has better insulation properties than say walls in a QLDer house with a timber stud frame sandwiched between weatherboards and VJs. It also depends on the orientation of the house.

depends on the type of tiles and climate but our old concrete tiles lasted almost 50 years and had been repointed and painted in the last 15 years but ongoing problems with waterproofing convinced us to replace the old tiles with Colorbond steel roofing, fascias and gutters...(we also vacuum cleaned the roof space and installed new ceiling insulation, replaced all the old electrical wiring and added a power point and light inside the roof for future inspections) not very glamorous but the $150 we made from recylcing the old wiring was a nice surprise after all the hard work and expense!

Do you have any photos, so that we can better understand what you want to do?