The sandbox tools allow you to create terrain models from contours with elevations and drape objects (roads, parks, buildings, water bodies, etc.) over the terrain model. If the snadbox toolbar is not visible, go through the following steps: Since the TIN is a smoothed surface, you can’t use the push/pull tool on it to create additional structures. Therefore, you must build any structures somewhere else in the model space and then move them down to the terrain. Once you have created a structure, use the move tool to move it down onto the terrain. Using the up, left or right arrows to constrain the movement to specific axes will help. You can also use the drape tool to drape a footprint on the TIN to help you properly place a structure. You can later delete that section of terrain if needed. For example, if you create a structure that drops below the terrain surface you will want to delete the section of the terrain model that covers that area. The Drop plugin allows you to arrange components on a 2D site plan with precision and then move them all down to the terrain with one click. Note, the objects must be components or this tool will not work. Select all the components you want to drop, right click on one of them and choose Drop at intersection. Source.