Create Custom Permission level in SharePoint
We always get into scenarios to allocate permission to users like contribute permission level without the ability to delete the files. So for this scenario you can use this article has a reference.
Click Site Actions à Site Settings
In Site settings page, Under Users and Permissions click on Site Permissions
In Site permissions page click on Permission Levels
Click on Contribute Permission level (Since we are going to customize the contribute permission level)
Click on Copy Permission level
In List Permissions un-tick the Delete items – Delete items from a list and documents from a document library.
Give name and Save the new SharePoint permission level (I have given Contribute without delete)
Newly added Permission level (Contribute without delete) will be now available in the permission levels.
Now we can assign the new permission level to users .