A complete search of the internet has found these results:
Have a great week is the most popular phrase on the web.
Both of these phrases have the same meaning. "Have a great week ahead" simply adds context that the week is coming up soon and might be be eventful.
2,030,402 results on the web
**Have a great week **and I'll see you next Saturday.
I hope you all have a great week at summer camp!
Did your sister ask if you will **have a great week **or not?
**Have a great week **and stay out of trouble.
We all hope that this city will **have a great week **this week.
I don't think he is going to have a great week after that injury.
240,209 results on the web
We have a great week ahead planned for all of you at this school.
I hope you all **have a great week ahead **of your big exam.
The coach told the team they have a great week ahead of them if they practice enough.
The campers knew they had a great week ahead of them, filled with exciting adventures and new friends.
The mayor told her consituents to plan for the** great week ahead**--it would be a milestone for the city.
A wise proved states that a person will never have a great week ahead of them if they do not embrace the poor weak behind them.