Adding roof to existing deck

Good morning,

Thank you for your reply.  The deck is 35' long (runs the entire back length of house) by 13' deep.  I intend to cover only part of it - say half.  I am researching post placement in several books.  I am removing decking and plan to place posts at each deck pier position perhaps, or maybe every other.  Sorry I am not sure yet but will try to follow whatever standard placement is, every 6' perhaps. 

I take your comment about roof rigidity to be consistent with my plan to NOT attach to house roof, yes ?

As of this morning, I am thinking of a standard open pergola design since those plans are easy to find, and easy to build.  1x2 or 1x3 strips on top for shade.  For rain cover, add hinged raisable rigid clear plastic sold in Home Depot (the corrogated sheets, mounted in hinged frames on top of structure, which could be lifted to open position from beneath, using poles).

In other words, divide project into two parts 1) basic pergola, which I think I can accomplish with my existing skills, then 2) tackle the rain protection separately, using a paneled approach, instead of a single roof.  This would give sunlight benefit of pergola, with occasional rain protection.

So next step is to research what the standard practices are for pole and beam spacing, then layer that on my existing deck measurements, taking into account that only part of the deck will be covered.  I expect to use 12' 4x4s (6x6s seem pretty huge) which will rest on concrete pads and be lagbolted to existing deck framing.  I may reduce post height depending on how it looks relative to roof height.  The deck overhead will definitely be higher than the roof edge.  I may add a minimal pitch for drainage.  Was thinking pitch UP from the house to the yard might be cool.  But pitch is a complexity that might be wise to omit, seeing as how this is my first project.

Thanks again.  If you have any thoughts, I'd sure appreciate hearing them.