are you trying a implementation?
well i would say plan the project first. Implementation is easy but if it does not serve any purpose it won't matter.
The main thurst In RFID is twofold
1) cheap cost with simplicity in design
2) and low power.
even if you planning a small project, it would be better if you try to think about the simplest idea you can think of to do the basic functions.
Best is go to a departmental store. ask them about the tags(they will show you the setup. Infact if you press a bit they will show the main reader and db also.. now this part depends on how good the person is

) ask him what his requirements are. He will say monitoring some 4-5k products. So that gives you basic idea of the bit size you looking for.
again there is multi bit and one bit implementation.
One bit is damn easy and pretty much useless now a days as it gives next to no info apart from whether the good is within or outside the range..(security) ,, multi bit is more inline used for inventory control.
either way you should start with a visit to a big departmental store.
SuperNova posted 2.2 minutes later:
btw practically speaking you will have to follow standards...
check out this site.
http://www.autoidlabs.org/