converting attic

Looking at coverting an attic to living space that has full oak 2 by 6 as floor/ ceiling of lower space with a 16 foot span. Just mainly want to put mattresses
on floor and clothes up there. Was hoping to use the 2 x 6s as the floor and put 5/8 osb on top with r19 insulation and lightweight drywall on walls but was recently told that i need to put in 2/10 along side each 2/6 which would inturn make me rewire the whole house as all the wiring is up there. Also have an hvac system up there that would need moved. really wanting to diy it and just use it as a loft for my boys. would add windows for access in case of fire. it has been cleared for any storage he said but at over 20,000 in labor for it all i am rethinking it. any advice would be great
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