Paddington Station is undergoing a revamp to provide better waiting facilities, more seating areas and food outlets, said Network Rail.
The work, costing around £20m, will include replacing the glazing on the roof with clear windows to let in more natural light.
The pillars, roof and steelwork of the Grade 1 listed building will be cleaned and repainted.
It should be finished in the next 18 months, Network Rail said.
The work comes as Network Rail predicts 61 million passengers will use the station in 2015.
First Great Western will also improve its ticket office, installing 12 counters and new ticket machines, bearing designs referencing the engineer Brunel.
source: BBC News