The move follows the completion of the first two speculative buildings toitalling 198,000 sq ft, both of which let to Virtus Data Centres.
The latest unit will be available as a single unit or for subdivision to create space for two occupiers.
Construction is scheduled for completion in late autumn 2018.
The announcement leaves just one additional 105,870 square foot unit available at Prologis Park West London.
Prologis Park West London is close to Heathrow Airport and easy access to the M4, M25 and M40 motorways. It is also located on the main fibre routes from London to Slough.