hi jules
perch and roach are both different in their feeding habits when large but smaller fish will munch maggots all day.
casters work even at this time of year for slightly bigger roach but not so well for perch at any time of year.
bread will catch all sizes of roach at any time of year be it flake or punched.
when the water warms up a bit the roach will start to eat sweetcorn more readily too. mid summer for really big roach you can't beat a small lump of stilton cheese.
perch love worms of all sorts even the little red worms, worms will also catch roach but if you have both roach and perch in a swim perch tend to get to it first.
you can even use multiple large lob worms for very large perch, i've had big perch on 2, 3 or even 4 worms stuffed onto a big hook.
probably the best really big perch bait other than lobworm however is a live bleak hooked through the top lip and allowed to roam freely under a light float you need to use a light wire trace (i use 15lb drennan 7 strand) when doing this though incase you get a small pike.
if you have and can fish 2 rods then i would suggest you set one up to fish worm using 3 to 5 lb mainline and 2 to 4 lb hooklength to a size 10 barbed hook if you can use barbed on the venue(i use drennan superspecialist)if you can't use barbed hooks on the venue then after you put the worm on the hook put on a very small piece of elastic band or the worm will wriggle off the hook , use the 2lb hooklength with the 3lb mainline for smaller fish about a pound.
then cast it in close to some weed beds and leave it alone.
then a lighter float set up with maggot on the other rod you will catch the majority of your fish on this maggot rod, you might only get one bite on the worm rod but when you do it will most likely be your biggest fish of the day.
as far as finding the fish roach will turn up almost anywhere but perch like structures in the water such as weedbeds marginal reeds changes in water depth, landing stages, over hanging tree branches especially if they are actually falling into the water, basically some thing they can hide in to ambush their prey
that should keep you going for a while.
let us know how you get on