Paul, cheers for the advice, I have ordered the 22.5" grate which should hopefully be here tomorrow.
I have now almost completely finished my smoker and can't believe how easy it's been. As promised, here are a few photos of the 'almost' finished product. Just need to wait for the thermometer to arrive and add the charcoal basket (which i'm making from an old washing machine drum).
Once I have added the thermometer and charcoal basket i'll add some more photos. Not the best craftmanship in the world but I'm proud of it so far