It's a good idea to have your first slide show an overview of the total project, so that the judges are able to orient themselves to the site. The main focus of your photos should be the landscape, not the buildings. Make sure there is no debris or litter, dead plant material, etc. If there is, clean it up. Morning or late afternoon is usually the best.
High noon is generally a bad time to take pictures.
Remember to look at the background. If you're not sure of the right angle, shoot from several slightly different positions and choose the best when the film is developed. Try to have something in the pictures to give a sense of scale. Include close-ups and pictures showing details as well as the overall project. Professional photographers come in all shapes and sizes - some even specialize in landscape photography.