Sirivha,
You don't say whether the drawings are just 2d plans & sections etc, or it is actually a 3d model saved in dwg format.
If it is 3d, you can try opening the dwg file using the 'Open Object' command found under 'File>Libraries & Object> Open Object', but I'm not sure if ArchiCAD can bring in the 3d model with sufficient control over the colours to be useful.
If 2d, place the 2d drawings on a worksheet using the 'drawing' tool, then use the 'Trace & Reference' feature to overlay this onto the model's plans and sections to make sure you are modelling things to the right size.
Either way, you may have to model the building yourself if you want to try out different colour schemes.
With regard to the fill problem you are having, you can't place a fill directly on a library part with the magic wand, only between the boundaries formed by Elements like slabs and walls etc. Most Elements and Library parts (objects) have their own fill settings built in. Check in the Settings - there should be some settings controlling the 2d representation or Cover fill.
Hope that helps.
