A few ponits that need to said.
1 - make sure any metal products used, ie. angle beads, mesh is stainless steel as people do not know that the galvanized metal products are for inside use only. DO NOT USE CHICKEN WIRE a product call EML should be used. Expanded Metal Lath
2 - if PVA is used make sure they are using exterior grade which is waterproof and must be mixed in with cement. Normal pva should not be used outside for this application as it is waterbased, for best results a product call SBR should be used and is not much more in cost.
3 - There is no need to pva between coats of render.
4 - Make sure any sand used is not all fine grade, the mix should be 1 fine to 3 or 4 medium grade sand.
5 - If the builders you have chosen want the work and are profesionals, they should have have supplied you with a work schdule discribing the complete contract from start to finish. If they haven't, Ask for it and to include products intended for use.
6 - Make sure the builder you choose has supplied the schdule, products to be used, any terms and cond;s plus a payment schdule. if you are happy with all of this get both you and the builder to sign and date both your copy and his as this will form a legal binding document which both of you must then fullfil.
Also as a general rule, if its not writen down in the contract its not included in the price.
hope this helps.
www.simplybuildbetter.co.uk, February 2010