Wow. What a neat find. I'm not familiar with Rollfast. But here are things to look for to figure out if you can find replacement parts:
If it has old rusty steel rims, you'll want to replace them. You'll either have to rebuild them yourself or hire a shop to relace them. Make sure you can find rims and tires in that size (possibly 26 x 1 3/8 ISO 590) with the correct number of spoke holes. See sheldonbrown.com for ISO sizes.
The crank will be either 1-piece (Ashtabula) or 3-piece cottered. The 1-piece cranks don't adjust very well but they are strong. Cotter pins can be a pain to remove and can get munged but they are workable and new pins are available.
Probably a coaster brake rear hub. Not too hard to overhaul. No gears or handbrakes to worry about.
You're probably stuck with the existing headset, bb, and hubs so make sure they are in workable conditions. As long as they are not deeply pitted or cracked, you should be able to overhaul them with new bearings and grease. Though a BB can be a major pita to open sometimes (warm up your torch).
Eyeball the frame for alignment. If it's been in a crash the frame or fork could be bent. But it looks good in the picture.
Oil is good, grease is better.
2007 Peter Mooney w/S&S couplers/Terry Butterfly
1993 Bridgestone MB-3/Avocet O2 Air 40W
1980 Columbus Frame with 1970 Campy parts
1954 Raleigh 3-speed/Brooks B72