Awnings Patio Covers engineered Patio Covers conform to  National Building Codes in 37 States.  Below you will find a list that gives you specifications that the patio needs to slope for a given span and maximum spanable distance per Live Load to pass inspection for most parts of the United States. Your local Building Department can and will inform you as to the Snow and Wind rating codes for your area. You want to tell them it is an Open Aluminum Patio Cover.  These will be the same as for your local company. They should have this information close at hand. Remember this information is for your benefit. A local non-direct third party is your best attempt as to what is required in your area, ie; if possible your local building dept.---you and your families safety is a concern of ours also.  Span in general is the unsupported distance between the structure and the raingutter - header or an intermediate positioned "C" or "I" beam.) Slope, that is required minimum in inches of drop ( .40" per foot of projection [allow ½" per foot of projection as a safe margin ) An intermediate positioned "C" or "I" beam with posts can be placed at mid-span of projection. By doing this you will reduce the span between supports and this will allow for thinner pans to establish your projection. This sometimes will require you to install footings for the patio cover posts.
Our Patio and Carports can be designed for Snow Loads of up to 60 lbs. per square foot and Wind Factor of up to 90mph.  Snow weights approximately 5.25 to 5.5 pounds per cubic foot of snow ( 12" x 12" x 12" ) which is +/- = 1" in depth of water on a 12" x 12" area. Some areas may have a slightly higher water content than 1".  The Patio and Carport Designed slopes below are based on the 3-1/2" Super 12 Pan ( Standard Aluminum Patio Covers).
Minimum Inches of Slope required for a projection ( the distance you want your awning to extend from your home ) = 3 -1/4 ", 9' = 3 - 5/8", 10' = 4" , 11' = 4 - 7/16 " , 12' = 4 - 7/8" , 13' = 5 -1/4", 14' = 5- 5/8 " , 15' = 6" , 16' = 6- 7/16 ". Remember your concrete patio slopes also. 
Examples are for a 10 pound per square foot and 90 mph wind factor design:
Patio pan thickness for the following projections .018 will span up to 16 '- 2", .024 up to 18' - 8", .032 up to 20'- 6" and .036 up to 21' - 4". We can engineer up to 90 MPH Wind Factor. This may seem quite an extreme for wind but this is designed to protect against the Blustery umbrella effect of the wind. 

Note: 
Exposure "B" has terrain which has buildings, forest or surface irregularities covering at least 20 percent of the ground level area extending one mile or more from the site.  
Exposure "C" has terrain which is flat and generally open.  Extending one-half mile or more from the site, in any full quadrant.