I'm hoping to change my front door, but because I live in a conservation area I have to apply for planning permission. Can anyone recommend a technical drawing app (for iPhone 6plus) that would be easy enough for a total novice to use just to create a simple image with measurements for the application? I don't want to fork out for idesign only to find it's idiot proof. I've attached the measurements and sketch I want to translate into something a bit more professional-looking 
to give you an idea of what I need. Thanks