You have to create additional tab for displaying custom fields in ME21N, ME22N, ME23N
Add custom fields in CI_EKKO, if custom fields are in header level
Add custom fields in CI_EKPO if custom fields are in item level.
Then use Exit MM06E005 for creating subscreen . Create a project in CMOD for this exit, create your custom sunscreen here . It will get displayed as additional tab in Header or item level