If you're printing parts larger than 100mm, even when using PLA on a heated bed (which doesn't allow much warping), you may still have some problems. Using ABS for big parts will certainly challenge most home 3D printers. Fortunately, Slic3r has a setting that addresses this problem, and you may find it useful for all sorts of parts.
The Brim option in the Print Settings tab provides a horizontal ring of extending perimeters on the first layer of an object. This option can be highly useful if the object you're printing is sticking to the base of your build platform or if an object's corners start to warp during a print.
The Brim option was invented mainly to help big objects stick to the build plate during an extended print. It can also be helpful, or even essential, if you're printing tiny objects that don't have a lot of surface area in the first layer. The printed brim peels away from a finished object, with minimal cleanup required.
