My brother has purchased a block of land and had a Porter Davis employee to oversee the block to see if they are willing to build on it - It turns out that they are not prepared to due to it having 'Slope'

I am definitely not a builder nor do I claim to know a thing about building but this 'Slope' I cannot see. I am totally clueless

What do they classify as 'Slope'???
Are there many other competitive companies who scrutinize the blocks to this degree or is it a Porter Davis thing

Anyone been in this situation? if so, what did you end up doing?
His heart was set on a certain design with PD and now that they are refusing to build on this block I guess it leaves him no choice but to 1) sell the block or 2) find another builder.