Select "Create Room-Structure-Niche" on the left catalog and drag it into the wall to add a niche. You can add niches in 2D and 3D views. After adding, select the niche and you can modify the length, width, depth, arch height and elevation height of the niche in the properties panel on the right. Changing the arch height would turn the rectangular niche into an arch niche. To change the materials of the niche, please use the Material Brush from the top toolbar to extract materials from other finishes, and apply them to the interior surfaces of the niche.