The state of the roof and external walls are usually the key factors in barn conversion costs. If they are in good condition, the conversion costs should be about 60% of new build costs. So if you were building to an average standard of £900 per sq m, the costs would be 60% x £900 = £540 sq m. However, this figure would increase
if the standard of the specification was improved. You should also budget about £10,000 for paths, drains, fencing and so on.