You would not use armour plate or indeed steel of the same thickness if you were building a replica (just give the external impression) . To do so would be prohibitively expensive and very few companies in the country would be able to fabricate in such scale. If you are doing this with the full support of the City Council and veterans organisations you may be able to aquire / buy a bare hull that has been on a range and rebuild a static vehicle from that, but still at great expense. If you are working for an offical body and or have a very rich benifactor, I would recommend you identify yourself as such if you want to be taken seriously by dealers / Museums.