Is there a standard angle that the walls on a Victorian style conservatory taper in at ?

I'm trying to work out the floor area and haven't got all the necessary meassurements. In essence it's a 4500 x 5000 rectangle, with the walls that taper in 1350 and that's the only figures i have !

If i knew the angles i could work out the area from there. I'm guessing its around a 45 degree angle ?

Also, is there any software that would be able to draw the floor / calculate the area for me ?

Thanks all.