[cypher]

That first raised house would be ok as a play house but as Serendipity says you really want a house with no base to sleep in, not sure if the top comes off that or not but if not it would be difficult to clean.
Of the other three the Pickles cottage is probably a big enough size for a robo but maybe a bit small for a larger dwarf like a russian or chinese. You would probably need to plastikote the inside of any wooden house to protect it from pee.
I agree a nice house with a flat roof is good as it doubles up as a platform or shelf for putting things on, the only problem with the Trixie one is that small space under the ramp if a nervous ham hides under there you have to take the whole house out to get to them!
A lot depends on your budget but Rodipet have some great alternatives if you can stretch to it!
The wheel looks like a P@H silent spinner look a like to me? Velma did a review here you might want to look at if it is.