In most cases, the location of your Pergola will be limited to one spot but it is possible to adapt the design to make it the most suitable for your particular requirements. As the sun is continuously moving the location and amount of shade that any structure offers will also be constantly changing. Deciding when (eating lunch outside, reading in the afternoon, entertaining in the evening) you are most likely to want the benefit from the shade is the starting point. You can then adjust the height and/or direction of rafters or crossbeams to make them perpendicular to the sun at that time of day. If you have more flexibility in the location of your Pergola then consider that the effects of the sun are usually most intense in the afternoon. This is when the ambient conditions have had all morning to warm up and as the sun starts to get a bit lower it will shine directly onto walls (as opposed to being higher in the sky). If you are using the Pergola to offer shade for the house as well, then placing it on the southwestern side ( in the northern hemisphere) will gain the most benefit.