Ok off the top of the head:
An espresso "roast" would be by ANY coffee (be it blended or unblended) *that is roasted to a point where it is suitable for use in espresso brewing equipment. This is usually referred to in terms of the COLOUR of the resulting roast, and that would be anywhere between a cinnamon colour to a black colour. Coffee roasted to a colour lighter than cinnamon (called "light roast") is not usually used to make traditional espresso coffee and it is therefore not an espresso "roast".
So the word "roast" in that context, would refer to any coffee beans roasted to atleast a cinnamon colour. The longer you roast the coffee, the darker it gets (as in baking bread or whatever, until you burn it and it has turned black).
In Australia, most commercial roasters like to follow the northern Italian tradition which is generally speaking, to roast their espresso "roasts" to a cinnamon colour.
The southern Italian espresso style roast colour is basically black.
An espresso "blend" is a blend of whatever beans from any particular origin, roasted as above, so as to give in the opinion of the individual roaster, a good "espresso" style coffee in the cup!
Any attempt by me to try and give you any more information than the above would probably just serve to confuse unnecessarily, so that should about cover it enough for the moment.
Hope it helps.