Each rabbit owner needs to shape the enclosure in a way it is easy to clean. Then you need less time to clean, it will be easier to do and so you may do it more often. Additional it will be easy to clean the enclosure in case of some illness when you need desinfectant or similar.
The underground is really important. Here you want to have something easy to clean, waterproof and simple to install. If you are experienced you may use flagstones/tiles, it is the cleanest way but not easy to install. Linoleum is the next best underground. It is simple to install, fluidproof and holds no toxic steams (difference to PVC, here you need to wait for them to dissappear before adding the rabbit). To avoid the rabbit eating it, it should end outside the enclosure, or with some additional wooden frame at the edge.
For the next step you need to know, that rabbits like to defecate where they eat. So they place their head onto the food and start defecating. This ensures the food stays clean... and it helps you to place the toilets! Toilets are flat bowls filled for example with wooden pellets and straw. Their surface has enough space for the rabbit to lay down inside as long as it is. Examples are the plastic bottoms of typical wired cages, or cat litter boxes without top/roof. Important are no sharp edges and maybe a step so the rabbit comes in and out easy. In the best case you simple need to change the filing of them once a week and the cage stays smelling good. Place a toilet under every hayrack, and place also the food bowl in one of the toilet-pans. If this feels not hygenic for you, you could add a little step so the bowl is higher than the litter.
Because rabbits have habits to use the same place again and again for defecation, you may only need to clean one of the corners of this toilets. But even if your rabbit uses different places outside the toilets, you will know them and you can place "pipipads" there. Pipipads are soaking fabrics covered with fleece in human-attracting-patterns (the pattern does not interest the rabbit ^^). This pads will soak the urin at the rabbits favourite places and you can wash them regularly.
Dependent how often you want to clean the enclosure (often the small spots, or less often all of the cage) you can also cover the whole underground with a layer soaking fabric and then a layer fleece. In this case you need to wash the whole fabric+fleece at once, but may have more time in between. There are even people, which have no toilet pan anymore and instead use all fabric&fleece.
The litter need to be well soaking AND friendly to the feet AND no risk for health. Risky are cat litters that stick together when wet. Rabbits would try to eat (all of the litters) and die because they stay as rock inside their belly. Also a risk are strong smelling litters because rabbits are sensitive with their breathing systems. You can cover well soaking litter with feet friendly litter. My best experience are wooden pellets covered with straw.
There are a lots of fabrics made for soaking. For example for babies beds, or for people who need special care in hospitals or retirement homes. You can search online, which kind is available where you live. Look for example for molton bedsheets. Important is that you add a layer of fleece. Fleece will not soak, so your rabbit will not get wet itself when running over the fabrics. As rabbits try a bit of everything you should have a close eye onto the fleece. It is not a risk for health if your rabbit tries to eat a small bit. But if it eats it regularly in high amounts, you need to find another way of handling the toilet-problem.
Additional: wall protection
Some rabbits spray urine to mark. This could also hit the walls inside the enclosure. Then you may want a protection there. Examples are transparent PVC or PET foils/covers also as wood or linoleum simple attached to the walls.
Important to think over:
Rabbit alone, good idea? In Germany it is not allowed by right anymore to care for a lonely rabbit. Minimum are two and also minimum space for them are 6 square meter (with the assumption they get daily free roaming time in a much bigger space like an appartment or a garden).
On this website (German) www.anni-sophie.com you can find pictures of the fleece-type of handling. If you use a translation software you may also get more information and hints how to handle things more easy. (For example to use a pillowcase for washing the pads so left over hay and similar will not stay in the washing machine.)
Please give a comment, if there are points I forgot or you need more information in :)