Hello RIU, i would like to build an underground growroom. I plan on digging a huge whole in the ground. Pouring a concrete slab. Then use cement blocks for walls. I will then insert rebar in the walls, then fill will cement. I am looking for suggestions on how to construct the ceiling as well as the door. This will be completely underground, so i need it water tight. Depending on how big i make the room will determine what size tent(s) i will be using. I plan on going all out with 4-6 1000w hps' w/cooltubes, carbon filters, co2, and ebb n flow system. I plan on using a silent diesel 6000w generator to power everything. I would greatly appreciate ANY comments and ideas. Seriously if you think you have a good idea to supplement my plans, please let me know. I want to go all out but, i want to be stealth about it. Criticism is welcome! Thanks and happy growing!