With Shared Ownership, you only need to put down a deposit on the share you're actually buying, so it’s less than it would be with a regular mortgage. The average Shared Ownership deposit is between 5-10% of the share.
Alongside your deposit, you'll need to put aside money for moving costs, stamp duty (if applicable) solicitors fees and leasehold fees. If you're buying a flat you'll also need to factor in yearly ground rent costs. Ground rent covers any building maintenance costs and upkeep of communal areas.