I'm making an underground tree farm, with a glass roof (don't know if it's still underground then). Just so sometimes I can get wood without worrying I'm detroying someone's trees or having to go outside in the dark. Also it's just a cool thing to have :). The glass roof will have a fence around it so mobs won't walk on it (I think mobs don't spawn on glass...).
Dimensions: 40x31 and 6 high The glass roof requires 1240 pieces of glass + wrongly placed glass & broken glass (creepers). That's 20 stacks. The fence requires 150 pieces of fence. That's 450 sticks. And that's 113 wooden planks. Which is 29 pieces of raw wood. The amount of blocks in total I have to remove to make the room: 7440. Just some information I thought you may want to know :). If you think any of these maths are wrong please tell me, thank you.