Hi Jon,
firstly a warm welcome to the forum & wish you well with your Roadster build,
its hard to give an accurate weight as each builder may have completed their car using different materials ( eg. floor ali/steel etc) but most cars seem to be around 530 to 600kgs,
tho if forum member "Slimtater" see,s this then i,m sure he,ll know the weight of his car, its a blade engined Roadster.
hope that help
cheers
andy