Rules On Roof Garden In The Workplace

[CharlieJack]

I've been asked to look into utilising a small enclosed roof area approx 8 x 17 sq m for staff to use on nice days.
The walls are about 8 ft high with pigeon spikes so there is no risk of falls from height.
The plan is to use low cost plastic furniture.
There are 2 entrances to it, from within the office where staff will not be allowed to use and another entrance which is the fire exit going down the stairway (staff would go up the stairs onto the roofed area)
My immediate concers/considerations are: securing/clamping down the furniture in case of high winds, (or brought back inside after each day), positioning the furniture away from the edges (to prevent gaining height to look /climb over the parapits), putting in place house rules regarding waste, keeping tidy, no smoking or drinking alcohol, some appropriate signage for keeping exit doorways clear (assuming they don't already have them), accessible only from 12:00 to 14:00
Would this be permittable as the previous tentants were able to use the area like this (probably on their own back without consulting any one).The existing company solely occupy the building.
I would be very grateful if anyone can tell me if I've missed anything?

[woofgang]

Landlord's permission? Will the roof bear the weight?