Gosh, those are some really attractive ideas. We have built cat sized snoozing shelves at a couple of window ledges, as well as real cat trees. From real trees, which garner some nice comments. I should say the OH did.
In two cases in our house I've taken steps to prevent climbing on certain shelves. One is above my computer monitor. When it was the big old square box type monitor Ginger used it to launch herself up to a shelf above and landed on it on her way down. She set off some pretty alarming rocking and rolling. Another place we've thwarted them is the shelf on which rest two lovely and expensive duck decoys.
Access to the top of three linked tall book shelves and from there to the top of a TV tower storage thing we've left to them, only modifying for the safety of some pottery we used to have up there. They love to sleep on top of that tower and look down on us.