Astropad is an app which promises a professional quality integration between your Mac and your iPad. Oh, and it’s built by two ex-Apple engineers.
Use the Mac creative tools you know & love, like Photoshop, with the touch experience of your iPad ~ Astropad
Start in Illustrator by creating a new document: File > New. I recommend starting by setting the dimensions to the default PowerPoint size of 10 x 7.5 inches or 720 x 540px, a 4:3 aspect ratio. Additionally, you should determine whether or not your client is also going to need a 16:9 template, the other standard aspect ratio for PowerPoint.
via Create a custom PowerPoint template – The Creative Edge.