This is what I have posted before and it's what I give my customers if they start comparing my material prices to those at the box stores. You really NEED significant markup to cover the REAL costs of providing the right materials at someone's home/business.

1) My level of knowlege of product quality/usefulness/ease-of-install was bought with trial-and-error (my time and money) and is worth quite a bit. In other words, I know what to use/not-use.

2) When you buy it from me, it's right there at your house. The things involved in that happening include:

a) Vehicle expense to drive to supply house/store
b) My time to travel and shop
c) Bookeeping and Accounting costs
d) Inventory time to make shopping lists (to make sure the truck is always stocked properly)

3) Other factors

a) Waste (if I buy a 250' roll and have 15' left over it goes to waste)
b) Items involved in installation that are not itemized on the bill
i) Nails, screws, anchors
ii) Connectors, staples, pig-tails
iii) Caulk, duct-seal, tape

4) Warranty - Buying from me means that I warrant the item for a reasonable period of time. If something is defective, then it costs me the following:

a) Labor and Travel to replace the part
b) Time and Travel to return the part

5) Tools - The cost of replacing tools is really proportional to the amount of material installed and not time spent on a job. Five hours of troubleshooting is no wear on my tools, but virtually every part I use puts some wear on a tool.

6) Time Cost of Money - All the money I have tied up in materials is NOT in a bank earning interest