Recently constructed a carport. You may find that local code requires 6 X 6 columns with concrete piers. PA where I live requires a minimum of 24" deep piers but, in the works are a 30" requirment (now law in states like NJ where codes are pretty strict). VA may be different. My carport was about 24 feet long, the piers are approximately 7.5 feet apart. The local home center or lumber yard could give you the skinny. In our township, the zoning & building inspector poke their noses into the project & start recommending ridiculous add-ons that are not required by national or local code. Hope this helps.