Using a triple integral to find volume

Jgalt
I'm supposed to find the volume of a solid bound by co-ordinate planes x=0,y=0, z=0 & surface z=1-y-x^2 and am having a lot of difficulty doing so. f(x,y,z) is not given so I am assuming it is one. I figure I should then take the triple integral dzdydx. Then, I made a 2D sketch for the xy plane to determine limits of integration. I took the ∫dz from 0 to 1-y-x^2 then ∫dy from 0 to 1-x, then ∫dx from 0 to 1, but I keep getting a negative volume so I must be doing something wrong... Please help!

$$\int dx dy f(x,y)$$