For each part that needs diffrent materials you need to assign it to a diffrent group, then assign a material to that group. Descriptive names will make it easier to change materials later, if you want you can use the same name for group and material, eg group name "TowerRoof" material name "TowerRoof", or you can have one material "tiles" and apply it to the groupes "LeftTowerRoof" and "RightTowerRoof".

Once you have the groupes and materials sorted out, apply the colours, textures, and any other material settings. Now export all the parts to one Wavefront OBJ file, ticking only "Include existing groups..." in the export options. Now open a new Poser document and import the OBJ you saved, leaving all the import options un-ticked (or you may want to use "Centered" and "Place on floor" if you have not already aligned the prop). Now save the prop to a props pallet.

Open the pp2 you saved in a text editor, search the string "Map" (case sensitive). Make sure Poser has saved the paths to any texture or other maps as a relitive path, colon seperated, and enclosed in double quote marks, these forms are ok:

":SomeFolder:wall.jpg"
or
":Runtime:Textures:SomeFolder:wall.jpg"

An absolute path, or one using back slashes, or without quote marks should not be used. If it has any of those you should edit it to one of the above forms.

You can now package the PP2 in a zip for distribution. Include any texture or other map files. You do not need an OBJ file as with this method the geomertry is stored internally in the pp2.