Ask nearby people who had work done you like who did it. Sometimes there will even be a sign out for awhile saying who the contractor was. If there aren't any ~recent jobs around you have noticed and admire then you will have to hook up with someone via a garden center, telephone book listing/ad, friend...go with someone you seem to get along with after you meet. If interviewing contractors about installation only get at least six estimates, pick one from the middle made by somebody you liked.

You can have one company design the work and another put it in. Other companies will do both. How much it costs depends on how big it is, who is doing it (different companies ask different amounts for the same job. If interviewing contractors...).