It was constructed entirely at the expense of his brother Thomas.

While the building was in progress, John Lombe hired various rooms in Derby, and particularly the Town Hall, where he erected temporary engines turned by hand, and gave employment to a large number of poor people.
At length, after about three years' labour, the great silk mill was completed.

It was founded upon huge piles of oak, from 16 to 20 feet long, driven into the swamp close to each other by an engine made for the purpose.

The building was five stories high, contained eight large apartments, and had no fewer than 468 windows.

The Lombes must have had great confidence in their speculation, as the building and the great engine for making the organzine silk, together with the other fittings, cost them about 30,000L.
One effect of the working of the mill was greatly to reduce the price of the thrown-silk, and to bring it below the cost of the Italian production.