There are distinct advantages to both low pitched and high pitched roofs
Low pitched-roofs require less material and therefore cost less. Also it's easier to heat and cool a building with a low-pitched roof. One major advantage of a low-pitched roof is expandability. If you ever add-on to your building you will be able to add more space while keeping the loss of headroom to a minimum.
Higher pitched roofs may add to the cost of the building, but can add performance to a building in a heavy snow region. Additionally, you can take advantage of extra space above. High-pitched roofs are less likely to leak and can add style to your building.