Hi Siddharth,
Thank you for your update.
We have prepared the sample based on your requirement, The below sample will show the CustomAggregate for computing "SUM" based on the checkbox column in the GridDataControl. Please find the sample in the below location,
Sample:
http://www.syncfusion.com/uploads/redirect.aspx?&team=support&file=SyncGDCSummaries-1389802218.zip Likewise, you can implement CustomAggregate for different scenarios.
Please let us know if you have any queries.
Thanks,
Rajasekar