Design ideas for mobile coop - a la Paul's Paddock Plan

Hello,

Having gone through the long thread about paddocks and moving chickens, I see there's a lot of different ideas about what one should have for chicken tractor/coop/temporary shelter for the flock, and I can't stop thinking about the possible designs for my own (future) chickens.

I'm in a somewhat unique situation in that I have a lot of forested (sloped) acres, but don't have much pasture or a big desire for a giant flock. I'm hoping to maybe have 3 -5 birds starting this year. I notice there is a WIDE variety of needs and plans amongst the group, and each situation is somewhat unique, but I thought it would be a good idea to have a thread focusing just on building and designing coops.

After buying into Paul's thoughts on moving paddocks for their diet variety, lowering feed costs and ease of care and cleaning, I want to build a coop that will move with the fence around a wooded area.

Not having any experience with chickens yet, my understanding about space and habits could use some advice from experts. Here's my crude drawing:



Notice the tray, looking a bit like an old tool box insert, would be filled with litter and thus the roost would act as a handle for easy removal and cleaning. the nesting boxes would also be movable, for cleaning.

Questions:
- what sort of head room do chickens need for a roost?
- am I making a mistake to have them roost next to the vent/screened windows?
- how much head room do they need to get around? ie, how tall does my roost need to be from the floor of the box?
- how much venting is too much? I was thinking triangle windows on each end and opening above the door on the front as well.


Tys

I don' recommend using the roost as a handle--it will be covered in chicken droppings (not everything falls to the floor, and is very sticky and icky to touch, in my opinion).