SharePoint Online: Create Permission Level using PowerShell

Requirement: Create a new permission level in SharePoint online site collection for contribute without delete permissions.

SharePoint Online PowerShell to Create Permission Level 

#Load SharePoint CSOM Assemblies
Add-Type -Path "C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\16\ISAPI\Microsoft.SharePoint.Client.dll"
Add-Type -Path "C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\16\ISAPI\Microsoft.SharePoint.Client.Runtime.dll"

##Variables for Processing
$SiteUrl = "https://crescent.sharepoint.com/"
$SourcePermissionLevelName ="Contribute"
$TargetPermissionLevelName ="Contribute Without Delete"

Try {
    #Get Credentials to connect
    $Cred = Get-Credential
    $Credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($Cred.Username, $Cred.Password)

    #Setup the context
    $Ctx = New-Object Microsoft.SharePoint.Client.ClientContext($SiteUrl)
    $Ctx.Credentials = $Credentials
    $Web = $Ctx.Web

    #Get the source permission level
    $RoleDefinitions = $web.RoleDefinitions
    $Ctx.Load($RoleDefinitions)  
    $SourceRoleDefinition = $RoleDefinitions.GetByName($SourcePermissionLevelName)
    $Ctx.Load($SourceRoleDefinition)
    $Ctx.ExecuteQuery()

    #get base permissions from the source and remove "Delete"
    $TargetBasePermissions = $SourceRoleDefinition.BasePermissions
    $TargetBasePermissions.clear([Microsoft.SharePoint.Client.PermissionKind]::DeleteListItems)

    #check if the given permission level exists already!
    $TargetPermissionLevel = $RoleDefinitions | Where-Object { $_.Name -eq $TargetPermissionLevelName } 
    if($TargetPermissionLevel -eq $null)
    {
        #Create new permission level from source permission level
        $PermissionCreationInfo = New-Object Microsoft.SharePoint.Client.RoleDefinitionCreationInformation
        $PermissionCreationInfo.Name = $TargetPermissionLevelName
        $PermissionCreationInfo.Description = $TargetPermissionLevelName
        $PermissionCreationInfo.BasePermissions = $TargetBasePermissions

        #Add the role definitin to the site
        $TargetPermissionLevel = $Web.RoleDefinitions.Add($PermissionCreationInfo)
        $Ctx.ExecuteQuery() 

        Write-host "New Permission Level Created Successfully!" -ForegroundColor Green
    }
    else
    {
        Write-host "Permission Level Already Exists!" -ForegroundColor Red
    }
}
Catch {
    write-host -f Red "Error Creating Permission Level!" $_.Exception.Message
}

Instead of copying an existing permission level and manipulating it, You can also create new permission level from the scratch.

#Create base Permission set
$Permissions = New-Object Microsoft.SharePoint.Client.BasePermissions
#Add permissions to it
$Permissions.Set([Microsoft.SharePoint.Client.PermissionKind]::ViewListItems)
$Permissions.Set([Microsoft.SharePoint.Client.PermissionKind]::ViewVersions)  

This script copies existing permission level and creates the new permission level
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