Removing the box in a box room

[cobblersmate]

Hi all
first post so here goes.
I need to remove a 4 foot cubed box in a bedroom to give a bit more space. unfortuneately the box covers the staircase with a slope of about 45 degrees from 8 inches below the lid of the box down to floor level. any ideas on what to do when the unit is removed. hope this makes sense
Cobblersmate

 

[big-all]

is this a void or is it set up to use
if its a void you will have to introduce sufficient timber so if a child stands on it it will support his weight
are the walls each side up to screwing battons to ??

my thoughts are 2x1" battons with scaffold boards[old or new] that will be strong enough to support a kid over a 4 ft span