How about this then:

If GL Code is 19, the max possible length of the data will be 22 (7+8+5 + 2 full stops)!

--BU is varchar(7)

--SUBSIDIARY is varchar(8)

--OBJECT is varchar(5)

--GL Acct is GL(19)

declare @a as table ([BU] Varchar(7), [ORDER_TYPE] Char(2), [SUBSIDIARY] Varchar(8), [OBJECT] Varchar(5));

insert @a values ( 'BU1', 'SS', 'Slumpco', 'OBJ1' );

insert @a values ( 'BU2', 'AA', 'Slumpco2', 'OBJ2' );

select

CASE

WHEN [ORDER_TYPE] = 'SS' or [ORDER_TYPE] = 'SP'

THEN [BU] + '.' + [OBJECT]

ELSE

[BU] + '.'+ '14350' + '.' + [SUBSIDIARY]

END

from @a