You can't risk assess static premises. IMO. You can hazard-spot, and / or manage by checklist, which may be what you are really thinking of. There is a case for identifying specific 'extra' elements of premises - this has been discussed before but can't recall any search terms - needing additional management, such as having lifts, or asbestos, or similar. It is the management systems required which is the focus. So in your situation - the grounds - slopes, nearby features such as water, parking arrangements, all may create some additional problems (not sure they would be 'risks' as such). Whether merely having a slope creates a risk very much depends . . . Who asked you and what are they expecting? Maybe they are under the impression EVERYTHING MUST be "risk assessed". Not true of course.