Does anyone know how to create these angles on cake tiers. Would you cut styrofoam to an angle and stick it to boards in between the tiers?

I have done this before exactly how you've described it - the cakes are normal shape and size, it's just the separators that are cut at an angle.
 

Thanks S, would you have used poly fake tiers or is there anything else you think would work better?

I used polystyrene cake dummies as they are lightweight and strong.
 

Thanks

 So here it is, my very first topsy turvy cake! I was quite pleased with it!! and the Bride was thrilled! which is the most important thing isn't it!!

Awesome work!!!!

Mine would fall over....lol

Thanks! I built it on site and had a dowel all the way through the tiers, so fairly sturdy!!