Chaining up 5v LED strips using 5v cellphone chargers
If you use 5V 2A power supplies then you will need 15 of them. The positive wires of each (30 LED) strip should be isolated from each other so that each supply is only powering one strip. It will work, but the mains wiring required is bulky and awkward.

Your second idea is not good because the power supplies won't share the load equally (some will put out slightly more voltage than others, causing them to deliver more current). It would be better to use a single power supply rated for at least 27A. Strips which are further from the supply should have thicker wires to minimize voltage drop. The downside of this option is that you need a lot of relatively thick wires.     

Using higher voltage and dropping it down at each strip with switching regulators would allow you to use thinner wires. Several strips could share the same power wires because the regulators will compensate for voltage drop along the line. 

However 5V * 27A = 135W, so two 12V 2A power supplies (48W) will not be enough. 135W / 12V = 11.25A. If the regulators were 85% efficient then you would need at least 11.25 / 0.85 = 13A at 12V. Again it would be better to have a single power supply that can handle the total load, rather than trying to parallel several smaller supplies.