It is difficult to convey the scale of something in a photo without putting it in context against something that we are familiar with. For example if you are photographing a big tree, putting a person near the tree can help the viewer notice the difference in size.
Having people in your photos can be frustrating. You wanted to get that pitch perfect image of the Taj Mahal and then someone walks in front. But having people in your photos is actually a good thing, providing a scale of sorts. Also think about having individuals in your images to help provide a story, inside of just the structure. Show someone gazing up at a skyscraper at it's majestic ability.