I have an old Hawk 1/48 scale mig15 and ti's cockpit is little more than a plastic slat the pilot sits on. I want to make the floor, front panel the seat I. I just help getting started. how do you match the contours of the model kit? I know I might be able to find a resin pit but I want to do this on my own.

Use a contour gauge.

https://www.amazon.ca/General-Tools-Contour-Gauge-Duplicator/dp/B00004T7RA/ref=asc_df_B00004T7RA/?tag=googleshopc0c-20&linkCode=df0&hvadid=292938355125&hvpos=1o1&hvnetw=g&hvrand=15671326695306889146&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1002604&hvtargid=pla-575181970552&psc=1

Cheers,

I use a contour gauge on larger things. Mine certainly would not fit in a 1/48 cockpit. I'd just stick a ribbon of putty against the fuselage wall. slide it back and forth to remove it - don't pull it straight out or you'll deform it. Now you've got the contour that you can trace around. Alternately, use a piece of A+B hardenable putty. Coat the fuselage with a very light film of oil, and form the putty against it. When it hardens, pull it off. Again, a contour you can trace around. And if you've already got putty lying around, it costs you nothing extra.

I have this exact gauge and it will work fine on 1/48.