The simplest method is the office partition, that SE posted. Though if you are looking for a plasterboard wall, door frame and door, you should contact FoodXchange contractor he specialises in renovation work for factory units. I cannot give you the number until Monday.
Though its very easy to knock up a stud wall partition yourself, the electric cable will have to be done by an authorised electrician. Try any local joiner, rather than a handy man or a small builder, as a walled partition have standard measurement for the framework. 4 by 2 inch is the norm and is done by joiners, not builders so a builder will outsource the work to a joiner.
Get familiar with the work, so that you know you are getting value for money, spacing behind must be to the set standard with plasterboard's set at centre of the downward supports.
Once you know its been done correct, you will know how to locate the wood support behind the plasterboard for the hanging of heavier items.
I have recently set up 6 office partitions, which is much easier than doing a stud partition and probably much cheaper too. If you are on a limited budget I would go for second hand office partitions.
http://www.ultimatehandyman.co.uk/partition_wall.htm
