A few things to consider... I dont mean it to sound like a lecture though ok... so bear with me
First things first - What is the size of the tank it'll be living in?
What are the results of your water tests?
If you've got 0 ammonia, 0 nitrite and your nitrates are rising, your tank is cycled and your ok to add more fish - stock the tank slowly though to give the bacteria time to build up with the new fish.
If your getting a plec ensure its a species that wont get too big - Bristle nose would be a great plec to start with - Avoid common plecs though as they will get big quickly.
Plecs add quite a bio load to a tank so only add the plec for a while and keep an eye on the levels - if your ammonia goes up - watch it carefully and start water changes, it means your tank bacteria wasnt ready for teh added load
Ensure you are feeding your plec - DONT follow the mind set that they are there to tidy up and clean the tank - its not true.
They need their own diet - and the diet required will vary depending on the plec you get
Have a look at your local store - get some pics of what they have if you can and come back to see what people recommend
Too many shops will sell you a common at the drop of a hat