fair % for finding discount materials/investing myself

[John Carpenter]

Hello
I am new first post.
I work for a man by the hour for over twelve years I get $15 per hour use own tools
So far this week I have saved him several thousand in materials,today it was at least2250/2300 on the lumber and plywood ,
Monday it was about 1600/$1800 and we have another lined up for the weekend (I hear about or get offered deals I call him and see if he wants it if so...I pay for it and end up having to wait and have remind him several times to get paid back and he stays behind on purpose.
I have been telling him he needs to give me a percentage to continue this.He thinks my pay should cover it. After today's deal. When I mentioned % he laughed, needless to say I wasn't happy

What's fair?

A little background......
He purchases property's generally we look them over and decide what to do
I figure materials needed and usually find best prices he purchases them
Minor things I work alone or run a crew, if problems crop up on other jobs I am not involved in they discuss it then its getting to where its always how would I handle it so I have to go there and deal with it
(He thinks my driving time and gas is free)
In areas where we have to have electricians and plumbers I deal with them and know inspectors
When we are not fixing up a property I am mr handyman for the rentals do every thing but collect rent

Have been Thinking about quitting for several weeks got serious about it today ,but only have a few thousand bucks put back
Have some materials and lots of electrical and plumbing

Think financially would be better off doing my own fix ups (On some projects I know purchase price the materials and labor costs permits taxes and later what price and terms it sold for and /or what it rents
It boils down to I think my piece of the pie should include something besides the crumbs
Just don't know if I should save up more and start collecting more materials or go for it
If I had the cash I would have quit today