I noticed today when grooming my rott boy that he has scaly bits and some hair loss on one of his elbows.  There is nothing on his other one.  It looks a bit like psoriasis but I am not sure.

He does have a preference for lying on hard surfaces but doesn't seem to have a preference for which side he lies on.

Any ideas what it is? 

It sounds like eczema but noone can be sure, even if we saw a picture, I'd visit the vet if there is hair loss.

In the meantime you could try using some Aloe Vera gel on it - preferably cold from the fridge, very soothing and perfectly harmless if licked off.

My rescue girl came to us with bald patches on both elbows, which sometimes irritate her so she scratches them and occasionally breaks the skin - Aloe Vera gel has worked really well for her, and a year later some of the hair is starting to grow back.

One of my geman shepherds had similar to this from the time he was about 18 months old and he always slept of hard floors. Vet told me that it was the same as we would get callouses on our hands if we did a lot of manual work as when he laid down he never laid on his side but with his legs out in front and his weight on his elbows. He told me to keep an eye on it in case the skin broke, it never did and didn't seem to bother him at all.

I will give the aloe vera a go and keep an eye on it.  He is a nightmare at the vets and needs muzzled and me holding him in a headlock before a vet can get anywhere near him so I will try a few home remedies too. 

He does throw himself down onto the floor and will lie outside on the concrete a lot so callouses sounds plausible.