Quick shapes question

I'm hoping I can explain this right ...

I want to make a shape - a square - but instead of the corners meeting or being rounded, I want them diagonals. Hmm, that doesn't sound right ... like if you had a regular square and cut the corners off at diagonals ...

Is there a way to use the rectangle/rounded rectangle tool to do this or would I have to make a custom shape by subtracting pieces ?!?

Thanks in advance!

I would make a square with the marquee tool, fill it with a color then use the polygonal lasso tool to make a triangle, used to cut the corners out of the square.

or you can make a rectangle/square marquee selection, fill it in, then make a square selection, and then go to SELECT : Transform Selection [or Marquee or whatever it says.] Then rotate the selection into a diamond and cut it out with that....

yup, that will work too.