i am building a teardrop camper, it will have a 100liter fridge/ freezer with 2x 150watt deepcycle agm batteries.

i plan to put 3x250watt solar panels on the roof. what size regulator will i need

Hi; 750 Watts of solar is working out at 62.5 Amps ( 750 /12 ) and a lot of current just for one fridge and a bit of lighting. At a guess you could get away with a 50 Amp controller, but why so big ??.In my own caravan it has 240 watts of solar, one 220 Ah agm battery and a 30 Ah solar controller. I run 2 x 40 ltr engle fridges, lighting in the caravan, tv,satellite receiver,  water pump on demand and have never run out of power. 

Is you fridge a 3 way fridge ( 12 Volt, 240 Volt and gas ) or is it a 2 way compressor type fridge ?? 

250 watt panels are large, have you taken into account twisting of the camper. Maybe better to use 6 smaller panels.

I can squeeze up to 11.3amps into the battery out of my 120 watts under perfect conditions. Usually around 7.6amps (3.8amps 2 panels in series) out of the actual panels into the controller. There is another 0.1amp load not shown in this screenshot, so output current is actually 9.0amps.

So on this screenshot ignoring the additional 0.1amp. 8.9amps/120watts x 750watts = 55.6amps controller output.

Maximum on my setup would be 11.3amps/120watts x 750watts = 70.6amps, but this is perfect conditions & very oversized wiring (6awg & also 4awg)

I originally had a 10amp output controller & it cut off at 10amps. Out of interest I got a 20amp controller to see if I could squeeze a bit more out of the setup. An expensive exercise, but I was interested nevertheless.

The controller will work less efficenty when running at its limit, so have some headroom.