When buying a house can you pay for it in straight up cash moneyy!

I suppose you could ? You could have the cash turned into a cashiers check( probably better).

Actual hard folding CASH, NO as this would trip massive alarm bells concerning money laundering.
As AC101 mentioned a cashiers check would be the preferred method.

I have seen this happen - certainly not with high end properties - but IRS DOES require that the form disclosing where the cash came from is required.

(Actually had a client some years ago show up with cash. Couldn't believe it but, again, it was a low end property. Do I think it's smart to wander around with a suitcase full of cash - no. The law firm representing the seller almost choked!)