This is just remix.
Since birds should have much more space for twigs and hay to make a nest, I've hollowed rock base and flattened it for easier printing. Similar clean-ups I've done with house itself.
Everything was scaled 250%. This is smallest, usable size - for smallest birds.

If your printer is big enough, you could print rockbase and house in single print. Otherwise you should glue it together after printing.

I have glued rock base and house together, and then screw it to the post with single bolt trough the opening - so I can remove it and clean - leaving rest on the tree. Roof is attached to the post from the back - no need to remove it.
The post has two holes up and two holes down for nails - to fix it on the tree. One nail should be fully nailed, another one just a bit more then a half - so when tree is growing, it won't rip of the post.
Use soft nails if you can, like aluminium or copper (for sawmill sake).

Object should be printed as they are now (unless this is how I've printed it). Rock base does not require any supports, roof requires only supports for the bottom "lip" - rest is ok without it. And the house requires support for pipes and windows.

You can use signs from original project (scale it up 250%).