Here is a starting point for a shoegaze reverse reverb sound. For reference, listen to "While You Sleep" by My Bloody Valentine. In general, you want to use reverse reverb before fuzz and/or overdriven amp while playing with the tremolo arm. The reverse should be fairly short - it smears out the attack and gives it a textural envelope.
We tried to keep it as simple as possible, with just a Context 2 and a fuzz into a clean amp. We used a smallsound/bigsound team awesome! fuzz machine (TAFM), because it has a slightly gritty clean blend. The signal chain is:
guitar --> Context 2 --> TAFM --> amp
The TAFM's clean blend lets some of the clean reverb sound through with the fuzz tone. That helps it keep its shape and makes the sound more complex. You could also use stereo output from the Context with one channel going through a fuzz and the other clean, into a mixer or two amps.
Here are the settings, with a screen shot of the Context web editor to show the delay settings: