Mr Punter

The lift and slide doors can be very good for airtightness. Also, they can be easily left open for a bit of ventilation. If you go for folding doors, do not go with a flush threshold as this seems the least airtight and most keen to snag on the ground.

400m2 is pretty epic. I take it that this is quite rural? Where I am yours would be worth about £1.7 to £2.1M and cost a minimum of £550k to build if you did a lot yourself. Quite an achievement.

I think you may need an Appointed Person to create a lifting plan, as this is not a straightforward lift. The plan should consider ground conditions, crane type, load type, load slinging, signalling / radios. Your own insurance should cover damage to the property or people, but you will need to take up the crane operators insurance as well. Crane operations are very tightly controlled by the LOLER regs and the HSE will come down hard if you ignore them and something goes wrong as a result. Another option is to arrange a contract lift, where the crane operator takes all the risk and plans the lift, but it is often very expensive.