Answer : SketchUp is an easy-to-learn design app for people who need to plan what (or where) they're building. It's a free download, so if you want to get started with interior design, there are plenty of tutorials online. But be warned that unless you've been trained in 3D modelling software, the concepts may seem a little counterintuitive! You can also download SketchUp for iPad which is ideal for architects and designers who want to do some quick and dirty sketching on the go.