Adding a porch roof over your deck can provide a space to enjoy the outdoors rain or shine.  The most basic gable end porches will shed water and snow and create a sanctuary from the sun.  Some designers add screen walls to preserve breezes while keeping mosquitoes at bay.  Tongue and groove cedar is the perfect material to finish a vaulted porch ceiling.  Vinyl or aluminum soffits can be outfitted to reduce maintenance.  Some high end porches even feature fans, canned light fixtures, and cable TV.
Gazebo structures can be built as standalone enclosed areas beside outdoor decks.  Octagon gazebos are popular and are usually built using cedar material.  Screen windows, doors, trim molding, and a variety of roof designs are available in easy to build kits. 
The size and style of your porch or gazebo depends largely on your lifestyle and your budget.