Company C's proposal says: "A deposit is required, additional payment
due at start of job & remaining balance due day of completion." Amount
of deposit is not stated.

Company B says: "Cost of Materials to be paid upon delivery. The
difference to be deducted from the total price of job." No deposit is
required. It doesn't specifically say that balance is due upon completion.

R1
Hmmm,
If you sign a contract, really you don't have to pay anything in advance
as long as you pay the invoice within a month after job is done
properly. Contractors in good standing has one month revolving account
from supply house. Also no local roofer's association? Members usually
have good track record. BBB? they don't have any legal tooth so they are
pretty useless if something happens needing resolution. You can use lien
hold back holding part of payment from the total invoiced amount
for certain period if the job i quite big involving large sum of money.

When I had my roof redone with ceramic coated meal tiles made in
Germany, work crew was from Ukraine who was familiar with this
particular product. 2 guys took 2 weeks and they worked like ants. I
could't see when they are taking break or eating lumch, just looked like
non-stop working. They were practicing safety precautions as it should
on 2 story house. At the end I treated them to a nice dinner at
neighborhood restaurant to appreciate their work. Then I paid full
invoice amount in certified check(~25K). This roof will last much beyond
my life time I am sure value of house invcreased somewhat as a result.

Since I found out those two kids are nephews of contractor who were
brought in from his old country. He told me they are the best workers
he had. I was lucky to have them.