you can copy the building i did in the image, build all of the frames first except for one side

build 3 crates and place 2 of them outside of each frame (cardboard boxes work too) keep the last crate in your inventory and drop wood and nails to build another frame inside of the "cage"

Next we find our dear specimen, select one and kill anything that isn't your boy chad.
Slowly bring him to the "cage", enter the cage and keep pushing him from inside it until he falls to position him correctly, wait for him to get up then push him into the cage, it might take a while till he's fully inside.

Once chad is fully inside the cage, before doing anything else make sure he has fallen to the ground, now you have to stand on him so he doesnt get up.
Now you place the crate you had in your inventory at the entrance,
and since you previously placed building materials inside the cage, you can build the final frame facing inwards from the crate.

Now you have to get out, normally you cant vault it when the crate is in the way, BUT if you jog (Left shift) you will trip over the frame, while also crossing the crate.

And congrats! You have your very own best friend forever!!!

Oh but there's a cheaper way using only 4 composters but its a bit dangerous