Yes agreed but it would be advisable to get registration after completion of Building and before Start of purchasing of Machinery (Capital goods).
In this way, you can avail Cenvat Credit for goods brought into the Plant as the Invoice Received shall contain the registration number, address of the concerned Central Excise division, name of the consignee, description, classification, time and date of removal, mode of transport and vehicle registration number, rate of duty, quantity and value, of goods and the duty payable thereon.as per Central Excise Rules 2002 and also as per Cenvat Credit Rules, 2004.
Also, please also go through the definition of Capital goods under Cenvat Credit Rules, 2004 as any goods used for construction of a building or a civil structure or a part thereof are excluded from the definition of capital goods and hence not eligible for Cenvat Credit.