I'm not saying don't use gravel, just that it will require more cleaning and upkeep, there is nothing wrong with gravel and crocs will often ingest small rocks to help mechanical digestion in their stomach (I'm unsure if there is a stage in life this process is more prominent). some of the principles involved in keeping turtles are relevant to crocs.
depending on how aesthetically pleasing you want the tank to look an upturned milk crate or similar will not facilitate a buildup of waste by allowing good flow, you could lay a section of astro turf over the top. Elevating a platform on bricks is another simple solution.
There is nothing wrong with what you have done, visually appealing enclosures can mean more or different maintenance/cleaning.