You mean an arbor? I don't see many arbors in Pennsylvania.. but I'm sure they are big in florida, California, Arizona where people get to use the yard all year long.
They are open, so as far as 'good'.. that's up to the person. If you have a fancy yard, live in a hot climate.. want that decorative shade.. then you'll think it's great.
If you have a so-so house, live in a moderate neighborhood and prefer rain and shade protection.. you might find it a ridiculous piece of architecture used by people with too much time on their hands... haha

Here is a link that might be useful: some complex ones

Thank you gorilla!! I didn't realize an arbor was more than an arched entry to the garden..... I live in Wisconsin and have a deck that faces the west. Entertaining in the afternoon is not possible in the summer. It gets so blasted hot and I would need several umbrellas to make it workable. I thought an "arbor" might be the answer.

Gotta do more research............see if they really work. I do have a "fancy yard" but I don't want a full roof over the deck nor, because of wind, will a retractable roof really do the trick especially when the sun comes below the roof.

karg,

The type of "roof" you are talking about is called a Pergola.

Pergolas are mainly for decorative purposes and to provide shade. They generally do not stop the rain from getting through.

You orient the boards (rafters) to provide shade from the sun depedning on how your deck/patio is orientated with respect to the sun and what time of day you use your deck/patio. For instance, if you use your deck around noon I would recommend closely spaced rafters at a 45 degree angle like this: ///////////. If you use your deck only in the morning or evening, the rafters can be farther apart and more verticle like this: !!!!!!!!!!!!!!

You will probably use something like 2x6s or 2x8s for the rafters depending upon the pergola support structure.