Adding a Lean-to on the side of a building. Anyone know of a good kit?

It's hard to locate anything viable on line and I cringe at lumber cost. If anyone has added one to an existing building from a company such as Versatube please tell me your story... It's gonna be a good size unit (protect my Pontoon, Jolene lol) so it's not something you find in aisle 9 at Home Depot.

Thnx,
JW