dropping tray, how wide?

don't know about height or width but you can use Aubiose or Hemcore for the droppings to fall onto and then you can poo pick it off each day.  Some folks use newspaper but it doesn't absorb much urine or smells.  You change the bedding material frequently though as you don't want a stink    With the width I'd err on the side of caution and you can always reduce it if needs be.

Your chooks might need a ladder but someone else will have more knowledge and someone will be along shortly 

mine always seem to sleep in the nesting box these days, now there's only two of them  So, it has to get poo picked every day so they're nice and comfy    They get clean bedding in it every other day.

I tried leaving them without any bedding in the nesting box just to see if they'd use the roosting bars (heaven forbid) but they stayed outside under their straw bales instead. I found them sound asleep when I went to lock them up for the night. I had to get OH to shine the torch so I could physically put them to bed. Dafties 

As soon as I put the bedding back in the nesting box they were fine. They do like their comforts. Just like us 

Try installing 2 trays that butt up directly under the perch. Make them a width that will allow the tray contents to slide off into a buckect so about 8 inches wide. This way it doesn't matter which way the chickens perch assuming they do!