أنت إنسـان عظيم
I assume you meant “a compliment.”
First let me go through the ProZ ritual of counter-questions: How do intend to use this compliment? In writing (using a formal style) or in a casual conversation (in a regional dialect)? If the latter, then what is your target dialect?
I will assume here that you will be using modern standard Arabic, possibly in writing, and that you intend to use “great” in a very broad sense (The American Heritage Dictionary lists 16 different meanings for “great”).
If so, then I would suggest ANTA INSANUN “AZHEEM or ANTI INSANUN “AZHEEM, depending on gender (notice that INSANUN AZHEEM applies to both genders. INSANATUN AZHEEMA has been used and is acceptable in many circles.
I prefer using INSAN in this context, rather than SHAKHS.
إنَّك إنسـانٌ عَظيم.
إنَّك إنسـانٌ جَليلُ القَدر.
ما أَجَلَّ قَدرك
ما أعظمَك أَيُّها الإنسـان.
I assume you are able to display Arabic text on your screen.
American Heritage Dictionary