i can imagine how hot it would get since it is in the attic... heat rises and thats at the very top... really the holes that you are going to make will help for air circulation but not nec lower the temps.

Lets say in the veg cycle... no problem you can keep the door open during those light hours allowing a lot of outside air to come in, but it is still hot air. Personally... the only thing i can think of is a portable AC in those conditions to stabalize the temp.

with nothing used to stabilize the temp, this is an option

lets say you can veg, if you do 18/6 you can veg from ligths on 6:00pm-12pm (18hrs and you can open the door) then lights off from 12pm-6pm (6hrs)

then when you flower... 12/12 lights on at maybe 5am-5pm (can open door) and off 5pm-5am (door must stay closed)
or something like that

GOOD LUCK and keep us posted