Sizing Calc but not as we know it

Hi guys
I'm new to the site and am looking for a bit of info on sizing a unit for a security lodge. I've used the dean and wood calc prog , but I have some minor doubts over the accuracy . Any help gratefully appreciated, as you will have noticed I did say security lodge , by that I mean approx 45% glass 50% brick 5% who knows. it has a ceiling of 2.9m but above that not an attic but a similar kind of void , the problem I feel here is that there is a tin cladded apex style roof. As you will appreciate dean and woods calc program is ok until you get the odd buildings like this.
Floor area is 5m x 1.9m . I can't use a rule of thumb due to the damn place being like a conservatory. I have tried to read as many threads as possible over the last hour but my eyes are glazing.
Thanks guys

size it for a high load 200 watts per m2

you will be close enough if not a tad over

cheers

richard

Much appreciated
Cheers
Steve

CIBSE rule of thumb is 125w/m2 which is on the high side so 200w/m2 as Richard suggests will definately cover a security building.

(Gymnasiums = 300w/m2)
(Server Rooms = 400w/m2)