Nice job :!: Although not an expert, I can share my thoughts and designs when I built my first hives last year. I looked around the web and adapted the features that I liked into my design.
The first one I made resembled the Crowder design, except I made it big enough to hang a Langstroth deep frame from the top bar to aid in the transition from a nuc into the TBH and added legs. I also put an entrance in each side, as my plan was to split it in two with a partition feeder, install a nuc in each side and hopefully overwinter both nucs. Come Spring I plan to move one nuc to another TBH and remove the feeder. As the colony grows, I can open up the 2nd entrance. I also liked the simplicity of the Crowder cover, simply a piece of metal roofing. Although the wooden covers look nice, they can be pretty heavy and ackward to move around. I really couldn't find any benefit in building a wooden cover.
Since the first one went so well, I got a little more creative on the 2nd design. Although the dimension are the same as the first, I decided to put the entrances on top to help cool the hive in the summer.
After experimenting with bottom-less Langstroth hives, I decided to make the 2nd version with a removeable bottom. I split the bottom in two with a brace in the middle and used two coroplast election signs as slide in bottoms. The feeder/divider sits of the brace so the two halves remain seperated for the time being. Come Summer, I plan to move the one nuc to another hive as with TBH#1 and remove the feeder. I then can pull out the coroplast and the hive will be bottom-less. My only concern is that they might build comb right out the bottom, in which case I will have to add some screen. Though in my Langstroth bottomless hive I never had that problem. The pictures aren't the best, hopefully I'll take better pictures while building the next one, but hopefully you can get the idea.
The coraplast slides in from the back.
Here is a view from the bottom.
Here is a view of the feeder/divider from the top. It is the width of 3 top bars and has a screened partition in the middle. Each side has access holes in the top of the sides for access. It has a piece of PVC (with screen) that allows easy filling. The PVC goes down bellow the side access holes so you can't overfill it too much without knowing it (otherwise you will fill the hive :roll: ) There is also a hole for a dowel 'dipstick' to check the level.
Hope this gives you some things to think about. Hopefully someday I'll get my website updated with better pictures of the TBHs.