ringworld is a pretty confusing map without looking at the editor, so I made a guide to help you. UV is very hard and has some 
sections that need some serious luck, lower difficulties should not be as much of a problem and will be pretty fun.

First fights are pretty straight forward, but you must save ammo and health. Grab the rocket launcher on top of the spire
and let things infight. If you have less than 5 rockets before pressing another button you will have a very bad time.
health is very scarce here, you can grab the health and armor in the revanent pockets but it's risky, I reccomend to wait 
until everything is dead. make sure you grab the backpacks before the bfg, they are easy to miss.

Things start to ramp up once you get the bfg. Grab the backpacks so you have enough ammo. There are some extra cell packs
near the top of the imp walls and a bunch in the two tan brick pillars, but they have 4 archviles each. I recommend
killing everything before the next part.

Once you press the three skull switches, the southern walls will open up revealing a bunch of cybers. Not that dangerous,
but about 10 seconds later hell knights come from every wall. Very scary part, but not horrible if you wait for the 
hell knights to leave the walls then bypass them on a cell charge platform. Again, you have plenty of ammo to kill everything,
but make sure to let they cybers die first, because it isn't infinite.

Next fight has 6 switches that you press at anytime in any order. All 6 lower a megasphere quickly, and archvile platform
in about 1 minute with an invuln, and start a big wave of spawning enemies. From left to right, here are what each switch does.

Switch 1: spawns a ton of imps and pinkys. Not hard but it really is a flood of them.
Switch 2: spawns cacodemons and pain elementals on the spire. Easiest wave but most archviles.
Switch 3: spawns cybers at the bottom and barons at the top. Hard fight.
Switch 4: spawns a huge mix of enemies on all sides.
Switch 5: spawns a massive army of arachnotrons and spider masterminds. They clog up spawners quickly so not very bad.
Switch 6: spawns a ton of revenants at the top and a ton of chaingunners at the bottom. very annoying.

big hint: try anything you can to save invulns. The more you have the easier the last fight will be.

once you press the last 6 switches on the archvile platforms, the last fight starts. A bunch of hell knights and cybers will
spawn, then the doors open and a invuln spawns on the spire. An insane amount of imps will be behind the doors. Use
an invuln to push through them and kill as many archviles and imps as possible. 

there are 3 keys, one to the left, one to right, and one in a cavity to the top. All three are protected by archviles.
once you grab 3 keys cybers and some other stuff spawn all in the outside area. lead them to the center or use an
invuln to get everything to infight. Cells and megas are everywhere but don't waste them. You will likely struggle for ammo
if you kill everything before the last cybers spawn, but there really is no way to run out otherwise.

the exit is in the same area the bfg was and needs all three keys.

hope this helps if you are lost or confused. All dificulty are implemented so make sure to try them for a more enjoyable experience.