Hi, I would make sure it was clean first ie, clear of cobwebs etc. After this use a good long haired sheepskin roller which should cover the majority of it and a brush to get the bits the roller misses and for the edges, window reveals etc. Has it been painted in the past. If so a couple of coats of Dulux weathershield should do it. If it hasn't been done the first coat may need to be watered down a bit to stop it soaking in to quickly, which will stop it from adhering properly. Then give 2 further coats.