I use Maxwell. The basic process is to apply the texture from your flooring material onto your floor (so if your .mxm uses a jpg image you'll use that same jpg image in your sketchup model). Get the scale correct in your sketchup model. Use the Maxwell plugin to link that flooring texture to your .mxm file. Export model and you should be good to go.
If I were to guess I'd bet you're applying a color (brown) to your flooring, linking that to your mxm and then exporting. Unfortunately if your SU material doesn't have an image telling it what scale to export out as it won't export any UV information at all.
-Brodie