Building the "box" is more a matter of your imagination. Essentially you just want to enclose the printer so temps can be more stable (and eliminate drafts) and preferably increased compared to room temp. For PLA it is not an issue for the most part unless your room is drafty and colder. There are plenty of creative example on line, for instance search for Prusa i3 MK2 enclosure.

This does not solve the ABS issues but will help reduce things. Mainly ABS wants a stable higher temp environment so it cools slowly to help reduce wrapping. A printer with the enclosure already is convenient but not mandatory.

I have the original Prusa i3 MK2 so my choice is obvious! I have not been disappointed. You can order kit or pre-built. there is a pretty long wait now because they are so popular.

There is a facebook group for this printer where you could ask questions (everyone may be a bit biased!). I'll try to post the name later when I can get it.

I might not worry to much about ABS to start with and first get used to PLA which is fairly straight forward to print. Get the fundamentals down and get used to the printer and how to solve issues. Working with ABS will just be changing what you have learned to fix issues. It is all doable!!