Need the comple mac casing as my on got messed up badly

It depends. There are several different generations of the 15" Unibody MBP, ranging from 2008 through 2012, and the cases differ between the generations. You have to use case components that match the generation of your computer.

If you post the last four characters of your serial number, we can look up the specific generation. Alternately, you can launch Applications/Utilities/System Information (or System Profiler, depending on your operating system), and click on Hardware. In the main panel, look for Model Identifier:; the code there (MacBookProX,X) will tell us which generation you have.

The primary case components are the "upper case" (the flat part on top where the keyboard/trackpad are mounted) and the "lower case" (the deeper part underneath with the sockets for power/sound/video/USB/FireWire/Ethernet/Thunderbolt/card slots/optical drive). In some generations, there are additional components.

2008-2009:

MacBook Pro 15" Unibody (Late 2008-Early 2009) Upper Case, MacBook Pro 15" Unibody (Late 2008-Early 2009) Lower Case, MacBook Pro 15" Unibody (Late 2008-Early 2009) Access Door

Mid 2009 2.53GHz:

[prodotto collegato mancante o disabilitato: IF161-089], [prodotto collegato mancante o disabilitato: IF161-027]

Mid 2009:

[prodotto collegato mancante o disabilitato: IF161-089], [prodotto collegato mancante o disabilitato: IF161-027]

Mid 2010:

MacBook Pro 15" Unibody (Mid 2010) Upper Case

Mid 2010-Mid 2012:

[prodotto collegato mancante o disabilitato: IF161-052]

Early 2011-Mid 2012:

MacBook Pro 15" Unibody (Early 2011-Mid 2012) Upper Case

iFixit sells most of the case components for Unibody 15" MBPs. You can use the Apple part numbers listed on the sale pages to search for other sources.