I'm not having a good day am I ?

If (big if) I am correct in assuming waste would be calculated using:

waste height * width + waste width * height

then:

I4:
=INDEX(F$4:F$7,MATCH(MIN(IF(($F$4:$F$7>=$C$4)*($G$4:$G$7>=$D$4),MOD($F$4:$F$7,$C$4)*$D$4+MOD($G$4:$G$7,$D$4)*$C$4)),MOD($F$4:$F$7,$C$4)*$D$4+MOD($G$4:$G$7,$D$4)*$C$4,0))
confirmed as an Array and copied to J4