I did make it from scratch, but I've seen premade nest boxes linked somewhere on this forum but it seems like they were rather pricey. I've got 2 boys that are going to help with the egg collection so i thought a shelf to put the 'egg basket' on would be a nice addition and I just built the nest box on that shelf using plywood. I used 2 angled shelf mounts from HDepot to mount the shelf and I left a little lip on the wall so that the nest material would stay in the nest box and hopefully not get pushed out. I'm still working out how to waterproof the nestbox roof where the hinge is, I think I'm going to reposition the hinge and see how that works.
I got the dog house from craigslist for $20 and the interior is 4'X4' square. My main concern was the nest box and ease of access. Thats why I went with the external option.