Three-Sided Pergola - the Snowflake Pergola

12' x 12' x 12' with flat snowflake roof

This structure has some great details:

It has large 10”x10” posts at the corners to accommodate the joinery.

The double plate around the perimeter is known as an outrigger. It gives more overhang and also acts as a valance where you could put lights for an interesting effect at night.

Vines grown over this structure could provide shade.

There is also a pavilion version of this design, with a pitched roof.