Individual Work Process memory are part of Roll Area and Extended Memory and also Heap Area Total. Now you can define maximum how much memory one work process can use using a separate parameter.
In my view your memory distribution should be like....Considering 76 GB of total memory you have
1. OS - 4 GB
2. Oracle
a. SGA - 22 GB [ db_cahce->12 GB, shared_pool->6 GB, log_buffer->4GB ] Later on you can execute buffer adviser query to allocate correct value for those buffers.
b. PGA - 6 GB
3. SAP Buffers (including ABAP buffer) - 6 GB
4. Roll first should be 1 [ Will enhance performance as WP will get continuous memory from Ext Mem]
5. SAP Extended Memory - 24 GB (TOTAL_SIZE_MB)
6. Heap Area Dia - 4 GB
7. Heap Area Non-Dia - 4 GB
8. Heap Area Total - 8 GB
ENjoy.