A secure skylight! And an easily cleaned floor! Remove as much as possible ie furniture cos it will get filthy,and damaged and hold all kinds of nasties. Secure the windows (we have chicken wired our sheds windows And can remove the panes for ventilation.)
Disconnect all gas, electric cos theyll peck.
Make sure they can get in and out easily (a little ladder or ramp with slats on it to stop them slipping)
They will need some roosting bars at least a few inches off the floor and a dark quiet corner for a nesting box (Old drawer is perfect)
\\yes, they should be locked away at night cos of foxes, rats and dogs, is your 'outside' secure as well?
Its a great idea, and you can at least stand upright in it yourself!