Top tube downslope angle

cancel the order.
save up for a better frame. carbon (parlee, crumpton) steel (vanilla, IF, Sachs, Pegoretti, Zullo)
Ti (makers who use shaped tubes to get over the low stiffness in large sizes)

do you even need custom? manufacturers/builders who offer 1cm increment sizes cover most sizes unless you are an odd size.

have you read the other custom frame thread?

Who said anything about bog standard tubes?