Sending Column Name As A Parameter To Aggregate Function

How can do this. Because my stored function contains same clause except colums name.So I want to use column name as a parameter but how can send column name and use it like Sum(parameter) function .

my procedure like this:

ALTER PROCEDURE [dbo].[ORNEK10]

@YIL VARCHAR(4),

@TEKLIF_TURU VARCHAR(255)

AS

BEGIN

DECLARE @N1 FLOAT

DECLARE @N2 FLOAT

SET @N1 = ( SELECT DEGERI FROM PARAMETRE WHERE PARAMETRE_ADI='N1')

SET @N2 = ( SELECT DEGERI FROM PARAMETRE WHERE PARAMETRE_ADI='N2')

SET NOCOUNT ON;

--I want to avoid using if statements for Sum() function

IF(@TEKLIF_TURU='BASKAN_TEKLIF')

SELECT TOP (100) PERCENT KOD1, KOD2, KOD3, KOD4, dbo.ORNEK10AD(KOD1, KOD2, KOD3, KOD4) AS ACIKLAMA,

SUM(BASKAN_TEKLIF) AS YILI,

((100+@N1)*SUM(BASKAN_TEKLIF))/100 AS YIL1,

((100+@N1)*(100+@N2)*SUM(BASKAN_TEKLIF))/10000 AS YIL2

FROM GELIR AS G WHERE YIL = @YIL GROUP BY KOD1, KOD2, KOD3, KOD4 WITH ROLLUP

ORDER BY KOD1, KOD2, KOD3, KOD4

IF(@TEKLIF_TURU='ENCUMEN_TEKLIF')

SELECT TOP (100) PERCENT KOD1, KOD2, KOD3, KOD4, dbo.ORNEK10AD(KOD1, KOD2, KOD3, KOD4) AS ACIKLAMA,

SUM(ENCUMEN_TEKLIF) AS YILI,

((100+@N1)*SUM(ENCUMEN_TEKLIF))/100 AS YIL1,

((100+@N1)*(100+@N2)*SUM(ENCUMEN_TEKLIF))/10000 AS YIL2

FROM GELIR AS G WHERE YIL = @YIL GROUP BY KOD1, KOD2, KOD3, KOD4 WITH ROLLUP

ORDER BY KOD1, KOD2, KOD3, KOD4



IF(@TEKLIF_TURU='MECLIS_TEKLIF')

SELECT TOP (100) PERCENT KOD1, KOD2, KOD3, KOD4, dbo.ORNEK10AD(KOD1, KOD2, KOD3, KOD4) AS ACIKLAMA,

SUM(MECLIS_TEKLIF) AS YILI,

((100+@N1)*SUM(MECLIS_TEKLIF))/100 AS YIL1,

((100+@N1)*(100+@N2)*SUM(MECLIS_TEKLIF))/10000 AS YIL2

FROM GELIR AS G WHERE YIL = @YIL GROUP BY KOD1, KOD2, KOD3, KOD4 WITH ROLLUP

ORDER BY KOD1, KOD2, KOD3, KOD4

END