what is and how do you mix up monocous render ?i do not know if is the correct spelling?

Question

this product is used to render the exterior of buildings

Answer 1

I suspect you may mean "Monomix" render - try this web link - http://www.arconsupplies.co.uk/pdfs/concrete_repairs/monomix.pdf#search='monomix%20render'
However, you can render a building using ordinary Portland cement and sand - possibly including lime but that is optional.
This site gives advice on mixes - http://www.diydoctor.org.uk/projects/mortarmixes.htm - most importantly note that the second coat must not be stronger than the first.
Rendering is skilled work - I would recommend you employ a builder to do it for you - but before you actually agree to employ them ask to see some work they have done recently - and talk to the people they worked for to see if they were a good firm. No reputable firm will mind giving you a few references like this - but if they don't seem to want to - ask yourself why, and perhaps find another builder.