My project is a special size trailer. dual 3500# axles but the bed is only 9' long with no floor.
The metal I will be needing (rounded up to the next foot):
3x2x0.120 tubing (tongue) 2 each @ 8'
2.5x1.5x0.120 tubing (side rails) 2 each @ 9'
2.5x1.5x0.120 tubing (cross rails) 2 each @ 7'
3x3x3/16 angle iron (adjustable spring mounts) 2 each @ 6'

(FYI, I can cut the metal to the correct length and I expect some waste. I know I can't order odd lengths.)

Now the questions about ordering the metal.
a) what are 'standard lengths'?
b) do smaller lengths have a larger per foot cost?
c) do the steel shops 'mind' small orders like this?
d) do most supplies have normal delivery routes and you just wait for the right day?
e) are delivery charges normally based on weight, number of items, or something else.
f) do I just call them up and say 'I need some metal to make a trailer' or do I need to know more about steel types and such?
g) are they used to newbies ordering stuff and so can guide one though the order process?