That is a factor of what you are building it out of and how big it is. There is no way of knowing without more information. Will it just be supporting itself or is it to be a trellis?
Typically the primary difference is that a pergola is attached to a building or a lattice. A gazebo, on the other hand, is a free standing structure. This is the big difference.
A pergola is a small structure that is probably more decorative than useful in keeping out rain and sun. See related links for building information.
I am building a pergola attached to the house. My span from house to support posts is 15 ft. What size raters should I use to prevent sagging?
You need to call your local town offices to check for local building codes.
Vinnie Pergola is 6' 1".
Pergola - album - was created on 2001-04-23.
Paolo da Pergola died in 1455.
Teatro della Pergola was created in 1656.
Antonio Mario La Pergola was born in 1931.
Edith Della Pergola has written: 'Opera at McGill'
Diocese of Cagli e Pergola was created in 1819.
Antonio Mario La Pergola died in 2007.