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The first one is going to require some agreement between players, although unless you have decided the railings are impassable terrain it shouldn't be an issue.
There is absolutely nothing wrong with the second. There is no rule requiring a base to be entirely on the terrain.
It totally depends on how you've decided to classify that terrain. For example, if you're saying that is a ruins, then any non-infantry model isn't allowed on an upper level of it unless it has the FLY keyword.
The big problem is that GW only has a very limited selection of terrain types (limited to what they sell), so when you're playing with something like this it's questionable how you're supposed to play it.
But rest assured, as long as you're not saying this is a ruin, then it's fine for any type of model to move on top of it.