I don't know what I was expecting the finished "coop" to look like, but this definitely wasn't it. It appears that you have a lovely exterior nest box and....a chicken ramp. I don't suppose there is any chance that he's not done with it yet?
If you can't afford much (any?) more for building materials, could you maybe measure the pieces that have already been cut and assembled, and go from there? It appears that the thing is held together with L-braces? If that is the case, it should at least be fairly simple to take apart and reconfigure as needed. I just can't wrap my mind around using the frame as-is and ending up with something that is the size you want, practical, and sturdy, but hopefully someone with more experience will chime in here with a brilliant solution. Maybe a trip to a Re-Store if there is one near you could help keep the cost down for the rest of the materials that you'll need. Barring that, there is the option of re-using wood pallets. I am no construction expert, but there are some good coop pages on here where pallets were used, and they can be had for cheap or free.