18s that are 7.5" will fit without rolling. 18s that are 8" will most likely rub, unless a very very very low profile tire is run. Also, rolling shouldn't require repainting to prevent rust if done correctly. To roll the fender lip, you can take it to a local body shop and they can do it, or you can DIY with a hairdryer, towel, and wooden baseball bat.
If you do it at home, you want to heat the metal with the hairdryer. it makes the metal easier to bend and reduces risk of cracking the paint. After metal is hot, roll the lip of the bat inside the lip of the fender, gently applying outward pressure. I suggest wrapping it in a towel to prevent scratches.
<span style='color:gray'><span style='font-family:Courier'>1995 e36 3 Series RIP
1999 e46 3 Series BURN IN HELL
2000 MR-S Roadster= Current</span></span>