Charli,
There are a few ways to roll your guards.
I think in your case you want to Roll guards (Still keeping your guard the same shape on the outside) but on the inside, it will change to give more clearance so the wheels and tyres do not scrub.
You just want to lower the car and have more clearance to fit the wider wheels.
You are not Lipping / Flaring or having bolt on guards.
The lower your car goes and the more wider you want your wheels, then you will need to start Lipping / Flaring / Bolt On guards.
Depending on how wide your wheels are and how low you go, you can get away with just Lipping the guard.
If the wheels are quite wide then you will have to Flare out the guards.
If the wheels are massively wide, you will need to Bolt On guards. (Like the white Old school GTR I posted).
Or the lower you want you car, you my need more clearance as you might already have wide wheels, you need more clearance.
If you look at the 2 R34 GTT's squareznboxez posted, that would be a good starting point as I think theyare stock guards.