All my fiber braids are combed tops. However, you will find the terms "roving" and "combed top" side by side in most of my fiber descriptions. That´s because the term "roving" is widely used on the internet and on market platforms when people look for unspun fiber. When you try to google "wool tops", you will most likely be shown a wide selection of garments, which doesn't help. So for visibility sakes, I use both terms to describe processed unspun fiber. 

Nevertheless, rovings and combed tops are two different fiber preparations. 

Roving is a carded wool, using a drum carder or hand cards to loosen up the fibers of e.g. a sheep fleece and bring them more in line. The roving contains short and long fibers and looks fluffier and fuzzier than a combed top.

A combed top is the next preparation step of the roving, being sent through large metal combs that remove all the short fibers and laying the long fibers parallel to each other, creating a smooth and dense strand of wool.

My fiber braids are made of combed fiber = combed tops.

For your first hand spinning project you may want to look for a wool fiber with a sufficient fiber length (staple length) and a soft to medium soft handle for a good grip. Try a sheep wool with a micron count of 24 or more, and a staple length of at least 4 inches (10cm). Fibers below 24 micron can be challenging as they usually belong to the very soft and smooth quality wool fibers. They tend to be rather slippery for a beginner and can be difficult to control while drafting the wool.

You can find 24-28 micron wool tops on my shop pages Hand Dyed Wool Rovings (combed tops)  & Spinning & Felting Fiber .

A gradient or palindrome (mirror image) hand dyed combed wool top, or a wool top with larger solid shade sections is a good choice when you want to control the color sequence and yardage to achieve long stripes, smooth color shifts, or achieve an ombre (color fading) effect using the fractal spinning method. 

As a wool top is a long strand of loose fiber it can be split lengthwise quite easily into as many thin and long strands as necessary. When you spin these strands from one end to the other, you will get a single ply gradient or self striping yarn. For a plied version, you can navajo ply (also known as chain ply) that single thread, just like the yarn in the picture (photos: courtesy of Jean Aycock). With this particular plying method the single thread will 3-ply onto itself, and it is therefore easy to predict where the colors will meet once plied. 

 
Another way of spinning a plied controlled gradient or controlled self striping yarn is to pull the fiber strand into short single color chunks. I personally choose the chunk method when I want certain colors to exactly (or nearly exactly) meet within the yarn, once it has been plied. I place the color chunks for two single threads in line next to each other on my table, so I can see where they will approximately meet while plying. The chunk size/weight of each color will need to be taken into account. 

Each chunk row is spun top to bottom onto 2 separate bobbins. I like using the inch worm technique (short forward draw) for very thin threads to keep them well-balanced and even. For thicker threads I prefer the long draw technique.

The yarn categories below are referring to commercially spun yarns, but if you have a hand spun yarn and you want to categorize it by its weight/yardage relation, feel free to use this list. 
I also included the wpi (= wraps per inch), which is widely used in the US. With this measurement you can calculate your total yardage for a 36-38 inch sweater (size M) by taking your wpi and multiplying it by 100 (wpi x 100). Add 10% for every extra 2 inch in size, or deduct 10% for every 2 inch smaller. Add another 10% for cables, and 30-50% extra for fair isle knitting. 

 
Weight                   Yardage/WPI             Needle Size
(aka)
_________________________________________________
cobweb                  690m/50g               1.5-2.5mm (US0-5)
(single/thread)      (767yds/1.8oz)

                                 wpi:40+
                                   
lace                         600-800m/100g     2-3.75mm (US 4-5)
(2ply)                       (667-889yd/3.5oz)
                                 wpi:30-40

light fingering         480-600m/100g        2-3mm (US 0-2)
(sock/baby/3ply)  (533-666yds/3.5oz)
                                 wpi:25-30

fingering                  400-480m/100g       2-3.5mm (US 0-3) 
(sock/baby/4ply)   (444-533 yds/3.5oz)
                                  wpi:14-24

sport (5ply)             300-400m/100g        3.5-4mm (US 4-6) 
                                 (333-444yds/3.5oz) 
                                 wpi:12-18

double knit              240-300m/100g       4-4.5mm (US 6-7) 
(light worsted/       (267-333yds/3.5oz) 
8ply)                         wpi:11-15
                  
worsted                   120-240m/100g        4.5-5.5mm (US 7-9) 
(aran/10-12ply)       (133-267yds/3.5oz)
                                  wpi:9-12

bulky (chunky)        100-130m/100g         5.5-8mm (US 9-11) 
                                  (111-144yds/3.5oz)
                                  wpi:6-8

super bulky         less than 100m/100g    8.0mm+ (US 11+) 

(polar)                   (less than 111yds/3.5oz)

                              wpi:1-5