I have a cold water tank on the roof. The 2 showers directly below have hardly any water pressure. How best can I raise the water tank i.e. stand it on bricks or do I have to build something?

Larger outlet lines from the tank will allow for more pressure to the heads, either that or smaller heads on the showers to restrict the flow.

Larger outlet lines from the tank will allow for more pressure to the heads
This will increase the volume to the heads but will not increase the pressure and restricting the flow at the heads won't increase the pressure ether. If this worked before then I'd check the shower heads for blockages. However, If you always had low pressure about the only other way to increase the pressure would be to raise the tank,thus increasing the head pressure or installing a booster pump on the outlet of the tank. Regards, Tom

SB hit the nail on the head. You could run a 12" pipe to the showers and would not probably notice much difference since the pressure would be the same. You only get 1# of pressure for every 2.5 feet or so of elevation, so unless your tank is 50 to 100 hundred feet up, you're just not going to get much. A booster pump would probably work wonders for you and would not be much trouble to install, nor cost an arm and a leg. Raising your tank is, to me, simply not a workable option. Bear in mind that raising the tank 10 feet (quite an undertaking) would only raise your pressure about 4#. You'd hardly notice it.