I was thinking of cutting the roof to match the tank but keep 200-300mm over hang just to minimize how much sticks out. I will need to seal most of those gaps somehow as the south half will be my warm control room.
I should be able to raise the floor a good 6-8" and still have head room.
I've no idea how thick the floor is, 2-3" maybe. Its a long way from flat so I will need to use some of that self levelling stuff they use on top of concrete floors to level them. I'll build a 1m form work around the pier location and just level that area. Evetually I may dig a hole and put in a concrete block to put the pier on if it needs it.
I'm a bit concerned about having an isolated section that it may tilt/move around a bit as the scope is moved around over time.
I'm putting the cutting of the doorway off till later. Thats the part that I could stuff up. At least if I stuff any of the rest up I can just go buy anthor length of timber and try again, not so easy with the tank.
But yes lots of fun and to many ideas. I think this might be work in progress for a long time.