When you have finished is most likely to be correct.

Both are correct, but depending on the context. E.g. - Give me a call when you're finished (doing something). - I started running right at the moment when you finished. I hope I've been helpful to you. But anyway is better if you wait for the answer of a native speaker.

With the first phrase you would be more likely to hear 'when you have finished (doing something) could you..............' - eg: 'when you have finished cleaning, could you help me prepare dinner'. The second phrase needs an endispiece to put it into context: You could imagine using it ......eg:.... 'When you finished in the garden yesterday, you didn't put the gardening tools back in the shed'.

Both are correct. "When you are finished" is in the future. "When you finished" is in the past.