Hi! I'm an IT engineer, that means I spent 5 years doing ER diagrams, I'm quite fond of UML, I'll be happy to send you some preview of my work if you provide me some more info on your project, the ammount of days and corrections will vary, all depending on the complexity of your idea, also the ammount of diagrams, like use case diagrams, ER, class diagrams, sequence or any other.
I'll be happy working with you in any term, long or short, I'm also open to skype interviews if you want to hold online meetings.
I also work with a team of developers who have worked in long term projects designing, developing, deploying and supporting IT products, if you are interested, we can discuss arrangements for an attractive price and not only design but develop and deploy your idea in an agile way.
Cheers!