With this guide to Empire of Sin, you will find out what hotels are for and how to build them.
The hotel is a building that in itself does not earn you money. It lets you bring new customers to the district though, which increases the profits from other businesses. So if some of the businesses in the neighborhood are still able to accommodate customers, then building a hotel is a good option.
Unfortunately, this solution is limited. Firstly, you can not build hotels whenever you want to - there can be only one per district. You must also have a proper level of synergy - you unlock a hotel construction only after erecting several different facilities. However, do not build it recklessly right after noticing that it has become available. Instead, look at the list of properties in the district and make sure that you are actually in need of additional customers.
You can find information about synergies on a separate page of the guide.