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Satya Ranjan MohantySatya Ranjan Mohanty 

why the formula(currency)field is not showing in fields to be aggregate while creating a rollupsummary field

Nishad KNishad K
Hi Satya,

Automatically derived fields such as current date or current user are not allowed in roll-up summary fields. This includes formula fields containing functions that automatically derive values on the fly, such as DATEVALUE, NOW, and TODAY. Formula fields that include related object merge fields are also not allowed in roll-up summary fields.

Some checkpoints for you to cross-check: About Roll-Up Summary Fields 
Hi Satya,

Currently this is not supported in Salesforce. As per the idea (https://success.salesforce.com/ideaView?id=08730000000Bra0AAC), this is under consideration. So we should see this being part of the feature capability soon.
Till then, create text/number field, make it read-only from page layout and update it using workflow. This field now can be used in roll-up summary field.