Oh, larger than I thought.
I find it intriguing and would like to see more pics from different angles to see how it is supported.
A pic of the inside might help to figure out why they aren't going in.
But back to your question....are your birds young?
I believe you said you recently acquired them and it could just be that they are not used to the new environment.
Chickens take some time to get used to new things, so I'd suggest just keep putting them in there and eventually they will probably figure it out.
I too would like to see more photos, I'm just intrigued myself.