What factors should be considered if an intermediate water tank at the middle height of a high rise building is going to be demolished, and we need to modify the water transfer system to increase head capacity to the basement transfer pump by installing a new pump in series with teh existing one wo that it can transfer water directly to the roof tank?
Removal of the tank could raise a number of questions:

Is the upper tank of sufficient volume for the whole building's storage?

If an inline booster is your suggestion, then the booster pump should be slightly smaller in flowrate than the primary pump, otherwise the booster pump could starve itself.

By feeding the whole building from the upper tank, the lower levels of accommodation will experience an increase in pressure. This may have to be reduced by PRVs. The pumps need to be interlinked to stagger the starting/and trip the booster pump if the primary fails for any reason.

A better option would be to replace the primary pump with a new booster set, taking the water all teh way to the roof in one step. Alternatively, if no high level storage is a legal requirement, a low level tank and variable speed booster set could supply the water direct to the consumer at a constant pressure, but again, the highest pressures will be experienced at the low levels of accommodation.

Source

Building Sustainable Design