Hi Jwalant
As per SAP Account you cannot maintain the fixed asset as inventory. If you manufacture the Fixed asset by own pass the journal entry for expenses related to the Asset (Asset WIP Account) and Capitalize the whole expenses amount.
Check the below it may helps you
Fixed Assets in SAP Business One Version 9 - YouTube
Fixed Asset - The Table Structure Finally Explained - SAP B1 Central
InSync Tech-Fin Solutions Ltd. Fixed Assets Management in SAP Business One 9.0, SAP B1 9.0
With Regards
Balaji Sampath