Collecting "environmental" data for the use of home automation is cumbersome and costly - if you choose to use the standard PCL components. A 4x analog input module for PT100/1000 sensors (750-460) costs EUR 280 (ebay price 02.2013). The price is astonishing even if you consider the easines of usage and programming. It is just 4 inputs!
As an alternative I propose to use 1-wire snensors, which are cheap and freely awailable. In order to connect a 1-wire network with the PLC I will use Raspberry Pi - a small computer working under Linux.