ztta/roll_first: Size of the Initial Allocation from the Roll Area 
This parameter determines the amount of roll memory in bytes that is allocated to a dialog work process, before SAP Extended Memory is allocated.
The graphic below shows the parameter’s relationship to the entire roll area (parameter ztta/roll_area).
Integration
You can find more information under:
Activities
The default value is platform-specific and is determined dynamically. This is the default value specified in transaction RZ11. This value should not normally be changed.
On 64 bit platforms, where there is sufficient extended memory, the default value of this parameter is 1, the work process therefore is allocated extended memory straight away.