Your biggest consideration will be allowance for wind and snow for the roof if that is a consideration for your location. It sounds as though you plan for 8 posts set 10 feet apart to be interconnected. Personally I would anchor the posts to concrete footings.

I don't know of any on-line sites with plans. Visit your local home centers and look at the garden books offered for sale. They will provide you with some nice ideas and basic plans.

Pergolas are generally designed for shade either with vines growing atop or with narrow boards anchored to the rafters. Ours is smaller than you plan but is resting over a paver patio. The footings go below the frost line.

Here is a link that might be useful: Pergola