We have 3 of ours that stay in crates while we are either away or sleeping. Gidget has one that is just right she has just enough room to move around and lay down and that is all, to this day if we go any bigger with her she will use it as a bathroom and she is over a year old. Jessie the 5 month old pup is in one now that is good for her sitting, laying, standing, etc...it seems a bit big, but she does well with it. Beau is in a larger one, he does well in his, but he is a big boy too, so he just has room to lay down, turn around, somewhat sit, etc.
We have 2 metal crates with a slide out bottom and 2 hard crates, sometimes tabitha will sleep in one, but it's rare. I like the metal one's only because they are easier to clean
and more ventilated IMO! We found that the metal one's are actually cheaper than the hard plastic one's as you go up in size. We only paid $55 for Beau's crate which is big enough for Dakota our 120+ pound rottie.
Jade is right they do make covers for the wire crates, We moved Jessie into the hard plastic one the other night as the weather is getting cooler, and with her being so young I wanted her to stay a little warmer, but she doesn't tolerate it well at all, I think she likes the metal one better because she can see everything around her
The only problem we have ever had with the wire crates, is when we had Reagan our foster GSD he actually pushed the top up enough to bend the bottom of the cage and got out with the door still locked......but he did well in the hard crate, guess he didn't like the wire one much