I think in that case, you shouldn't get a Guinea Pig at all. Guinea Pigs live in herds and enjoy each others company they are very social animals and enjoy interacting with one another.
In my opinion it is not fair to put an animal who normally lives in a herd on it's own granted some members may have pigs on there own perhaps they didn't know better at the time, the pigs fellout or the pig doesn't get along with others even then you will find they live next door to another pig or they are the centre of attention in the household.
If putting a ramp in I would do it so not steep, and put a side/banister on it to prevent the guinea pig falling off.
I would probably make the sleeping area 1' of the total width of the hutch leaving 3' as the day area.