User blog comment:Johnnyate8/please help with gta story mode/@comment-25368842-20150713015413

As stated here, upgrades at Los Santos Customs are unlocked as you progress through the Story Mode Missions (and Online as you rank up). You can't just get it all without earning it.

As far as the free garages, that only applied to the original (PS3/X360) version of the game for Social Club members. PS4/X1/PC users have to pay for the garages and DLC vehicles.