LOL Luc!
Leave access around entire tank. Don't make a wall you can't get in between.
When ordering acrylic, have them double check the size before shipping.
Check the weather before setting a delivery date for 400 lb. piece of plastic.
Apply Dow 795 to acrylic AND frame. Don't try to squeeze in in afterwards.
Measure the room and use dimensional lumber/plywood standard sizes. This eliminates odd cuts and wasted lumber due to scraps.
Calculate how many cuts you can get out of a length of dimensional lumber/plywood. In example, if you have 30", 12", and 11" pieces, you can cut 2 30", 2 12", and an 11" piece out of one 96" board. 30 + 30 + 12 + 12 + 11 = 95 (the inch or so left over covers blade width between cuts with a little scrap.
Make sure you have equal clearance on all walls if you're going to put your acrylic in the middle of the floor before you build the bottom of the tank.
Build the bottom of the tank before having acrylic delivered if at all possible.
Finish the entire room before starting construction on the tank.
Layout filters, tank, lights, etc. before you buy any materials.
Measure the materials at the store. Don't assume they are the size you think they are.