Its fine to propagate lager yeast at room temperature, especially if you decant the starter liquid.
Just make sure you know the yeast from the bottle you are culturing from is the breweries fermenting yeast and not just a bottling yeast.
"If you do it right, brewing is about ideas. A big impression can be made with brute force, but sometimes a whisper speaks louder than a shout." - Randy Mosher
Primary: Citrus Wheat Experiment/WLP029 & WYEAST 1056