Building a spare room in your basement works well for those occasional visits from out of town friends that pass through on business, or for the eldest child when your family gains another member when you are living in a three or four bedroom house. In addition, if a member of the family works that late night shift a bedroom downstairs away from the daily traffic works well for their privacy.
If this is the case for finishing a basement, it is wise to have a window put in for extra lighting in addition to using cedar in the closet, to help preserve clothing. As for bedding, a trundle or a Murphy bed can both work out well depending on the need. With a trundle, you can have two beds because of construction where one slides under the other. With the Murphy bed, you gain the extra floor space when the bed is not in use.
Once you have a finished basement designed as a usable bedroom the décor is an open gambit of choices. However, plan on what items you wish to furnish it with before the project is finished, such as a large screen TV, gym equipment and such can damage walls if not careful moving them in after the project is completed. Of course, this is dependent on the size of the basement allowing the renovation and the storage of these items to occur simultaneously.