Try something like this
select Cast((SPGI09_EARLY_OVER_T – (SPGI09_OVER_WK_EARLY_ADJUST_T) / (SPGI09_EARLY_OVER_T + SPGR99_LATE_CM_T + SPGR99_ON_TIME_Q)) as varchar(20) + '%' as percentageAmount
from CSPGI09_OVERSHIPMENT
I presume the value is a representation in percentage - if not convert it to a valid percentage total, then add the % sign and convert the column to varchar.