SketchBook is great for when you need to doodle something on your iPhone. I love Paper too but it's iPad only.

Its my favorite app on my phone it helped me grow my Instagram following to massive 15+ thousand followers. I have made some really cool stuff with the help of it. You can check them on my Instagram http://instagram.com/shikeb

That is actually a nice app, but seems like for beginners. Hard users are using autocad and other "heavy" software which was produced by Autodesk. But you still get get Autodesk license for cheap, considering you can't say they have inexpensive software.

My wife made some really amazing stuff with this app last night. She likes it.