Custom fabricated floor frames for custom cars and hot rods.  The chassis is the foundation and the floor frame is what everything hangs off. The way the floor frame is bolted down has to with stand a car accident, it is a really important piece of the car. Some floors are just tin and bolt to the chassis, then the body bolts through its tin base to the chassis, I would suggest this is on the weak side. A properly steeled out body needs a sound floor as a base structure.
   
In my opionion the floor frame of a hot rod body needs to be strong enough to mount the seats, seat belt anchor points and provide enough rigity so you can lift the body off the chassis and not have it flexing. It needs to tie into a framed firewall and have strong out riggers to pick up the A, B and C pillars.
   
The examples in the pics show both floors under construction. Price is indicative of the time involved.
 
All work is done at an hourly rate + parts + materials.