Home smoking

[Goodlife1970]

My OH is building a brick bbq/smoker,the idea being that when the bbq isnt in use we can smoke our own meats ect. The design is basically a large bbq with a chimney,two steel bars (for hanging the meat from) and a soot trap door for access.How high should the chimney be to allow for cold smoking? We dont want to cook the meat just smoke it.Also are any hardwood chippings acceptable as although we dont have much in the way of oak we do have lots of ash.