One huge advantage with RTAs is the same coil can last a really long time, usually with stock coils you have to change them frequently because they become so caked up with gunk or the cotton gets burnt and to carry on vaping them is just a waste of juice because there is either little flavour or a nasty burnt taste from the cotton.
With an RTA you just pull out the cotton, clean the coil (I just glow the coil and immerse it in a cup of water - the crud falls off completely after 2 or 3 dips) and rewick - the same coil can last months.
Sweet juices kill stock coils fast, but this isn't an issue with RTAs as the cost of rewicking is a few pennies.
I have a lot of rebuildable attys - when I feel like using a different one I just pull the wicks and clean the tank leaving the coils in place and take another atty off my shelf, 90% of the time it will already have coils fitted from the last time I used it and its good to go after a re-wick. I'm currently vaping a Goon 25 RDA - the coils in this tank have been there for over 3 years and still good, but I estimate I use the same coil/coils for about 3 months total vaping time before I scrap them, If I'm in any doubt I change the coils - but a 15ft spool of premade clapton or fused clapton wire is only about £5 if you shop around and that will make 40 coils. I don't vape mesh as I like the heat from bulkier complex wires - but the cost of a pack of mesh strips is minimal compared to stock coils.
Personally All you really need to start building is a pair of snips, things like screwdrivers and allen keys come with the tank. They tend to be crappy quality but they are cheap to replace.