Your code was close to what I needed except for the eventstartdate need to be in date format(Not just year or month or quarter number)

BEGIN

;with Vol_Aggregatedata as

(Select CASE WHEN @ipperiod = 'day' THEN CONVERT(char(10),EventStartDate,126)

WHEN @ipperiod = 'week' THEN dateadd(week, datediff(week, 0, Agg.EventStartDate), 0)

WHEN @ipPeriod = 'quarter' THEN dateadd(qq, datediff(qq, 0, Agg.EventStartDate), 0)

WHEN @ipPeriod = 'month' THEN DATEADD(MONTH, DATEDIFF(MONTH, 0, Agg.EventStartDate), 0)

END as Eventstartdate,

Agg.ProductTypeID,

Agg.ProductTypeName,

Agg.LoanProgramTypeId,

MIN(MetricValue) AS MetricValall ,

SUM(SampleSize) as SampleSizeall

FROM [Reporting].[AggregatedRatesforWidgets] Agg with (NOLOCK)

WHERE Agg.EventStartDate >= @ipstartdate

and Agg.EventStartDate <=@ipenddate

and Agg.LoanProgramTypeID= @ipProgramtypeID

GROUP BY CASE WHEN @ipperiod = 'day' THEN CONVERT(char(10),EventStartDate,126)

WHEN @ipperiod = 'week' THEN dateadd(week, datediff(week, 0, Agg.EventStartDate), 0)

WHEN @ipPeriod = 'quarter' THEN dateadd(qq, datediff(qq, 0, Agg.EventStartDate), 0)

WHEN @ipPeriod = 'month' THEN DATEADD(MONTH, DATEDIFF(MONTH, 0, Agg.EventStartDate), 0)

END

,Agg.ProductTypeID,Agg.ProductTypeName,Agg.LoanProgramTypeId

)

Select

vcy.EventStartDate as EventStartDate,

vcy.ProductTypeID as ProductTypeID,

vcy.ProductTypeName as ProductTypeName,

vcy.LoanProgramTypeID AS LoanProgramTypeId,

'ALL' asLoanstate,

vcy.MetricValall as MetricValue,

vcy.SampleSizeall as SampleSize

FROM Vol_Aggregatedata vcy

order by Eventstartdate ,loanstate

END