Wow! Your questions are impossible to ball park
The answer is - it depends. It depends on so many different factors that it simply cannot be ball parked with any degree of accuracy. For Sheep, I recommend the book "In Sheep's Clothing" which gives average fleece stats for a good number of popular breeds of sheep, along with much info on spinning, selecting fleeces, processing, etc.
As to how much roving you need to buy to weave a scarf - again, it depends. First, you have to know how much yarn you need to weave the scarf. Which means that you need to know the on-loom dimensions of the scarf + your allowance for take up, shrinkage, and loom waste (which will be less if you use a dummy warp for the waste portion). Once you know the yardage needed for the scarf, then you have to figure how many yards of that sized yarn you can spin from an ounce of the chosen fibers. Then you can figure out how much roving to buy.
There are 2 articles on the main Bellaonline spinning site to help you through the process of figuring it all out:
How much Fiber Do I need? and How much Yarn Do I need? Another article, Spinning to a Size, gives info on how to spin yarn to the exact size you need.
Or, there is the quick and dirty "eyeball" it method
First, spin the yarn. Then measure how many yards of yarn you have. Determine the width and length of the scarf, adding extra for takeup, shrinkage (I figure this at 10% of length) and loom waste (or plan to tie onto a dummy warp). My average loom waste is 27 to 36" depending on which loom I use. Remember to add more length if you plan fringe, or you can plan to use loom waste for the fringe. Then figure your sett and calculate how many yards you will need for the warp. Now figure how much yarn you will need for the weft - the length of each pick plus allowance for takeup and shrinkage (I use 10%). Add total yardage needed for warp + total yardage needed for weft and you have the total amount of yarn needed. How much fiber you need to spin that amount of yarn depends upon how you spin