Transact-SQL Group By Clause

I am writing a rather complicated query and have run into problems..
I seem to have the query correct so far but i'm unsure how to resolve
the problem of what the call the group by clause.  Here's the query
I'm only concerned with the area surrounded by ***(added for viewing
purposes only)
I need to name this part in the Group By Clause.

My Question..do I need to add the whole select part into the end of the
Group BY or can I give it an alise??

CREATE Procedure ROYALGetStockByPeriod

@StartPeriod int  , @EndPeriod int , @StockCode varChar(20)

As
     SELECT SM_STOCK_CODE, SM_Location ,          
     SUM(CASE SM_Status
          WHEN 'I' THEN (SM_Quantity * -1)
          ELSE SM_Quantity
            END) As TotalQty,
     ***CASE SM_Location
          WHEN 'ORC' THEN CASE WHEN SUM(CASE SM_Status
                         WHEN 'I' THEN (SM_Quantity * -1)
                         ELSE SM_Quantity
                               END) / SUM(CASE SM_Status
                              WHEN 'I' THEN (DET_NETT * -1)
                              ELSE DET_NETT
                                     END) > ST_CalcPrice THEN  SUM(CASE SM_Status
                                                  WHEN 'I' THEN (SM_Quantity * -1)
                                                  ELSE SM_Quantity
                                                        END) / SUM(CASE SM_Status
                                                  WHEN 'I' THEN (DET_NETT * -1)
                                                  ELSE DET_NETT
                                                         END) *10 / 100
                                             ELSE
                                                    SUM(CASE SM_Status
                                                  WHEN 'I' THEN (SM_Quantity * -1)
                                                  ELSE SM_Quantity
                                                        END) / SUM(CASE SM_Status
                                                  WHEN 'I' THEN (DET_NETT * -1)
                                                  ELSE DET_NETT
                                                         END) *5 / 100
                                                  END
                                                  END,     ***
     DET_NETT As SellingPrice
     FROM GMCPUBS.dbo.STK_MOVEMENTS
     INNER JOIN GMCPUBS.dbo.SL_PL_NL_Detail
     ON GMCPUBS.dbo.STK_MOVEMENTS.SM_Order_Link = GMCPUBS.dbo.SL_PL_NL_Detail.DET_Order_Link
     INNER JOIN Royalties.dbo.tblStockMain
     ON GMCPUBS.dbo.STK_MOVEMENTS.SM_Stock_Code = Royalties.dbo.tblStockMain.ST_Code
     WHERE SM_STOCK_CODE = @StockCode
     AND SM_PERIODNUM >=
     CASE SM_Location
     WHEN 'Lew' THEN @StartPeriod
     WHEN 'ORC' THEN @StartPeriod
     WHEN 'SCH' THEN @StartPeriod
     WHEN 'STE' THEN (@StartPeriod - 3)
     WHEN 'CAP' THEN (@StartPeriod - 3)    
     END
     AND SM_PERIODNUM <=
     CASE SM_Location
     WHEN 'Lew' THEN @EndPeriod
     WHEN 'ORC' THEN @EndPeriod
     WHEN 'SCH' THEN @EndPeriod
     WHEN 'STE' THEN (@EndPeriod- 3)
     WHEN 'CAP' THEN (@EndPeriod- 3)    
     END    
     AND SM_Location IN('Lew','Orc','Ste','Cap','Sch')
     AND SM_Year = 'L' AND SM_Type = 'S'
     AND SM_Status In('I','O')
     GROUP BY SM_STOCK_CODE ,  SM_Location , DET_NETT
         
     RETURN


Thanks in advance

Scott