you can use a String Attribute which contains a calculation.
This calculation checks the requirements and is showing the information required, based on the checks in the calculation.
You then can use a window calculation to only show this attribute when there is a message present.
The same window calculation can make an attribute mandatory to prevent the window from being saved as long as the checks have not been met.
Thank you for the help. I still have a small confusion whether the String that contains the message will be displayed on a field in the window or at the top of the window.
it will be displayed on the window where ever you put the control for that string attribute on the window.
This control follows the normal design principals of any other attribute.