I want to make a hat for my friend’s partner, he’s South African and I found a pattern for a springbok and thought I could use that and in cooperate it with some green wool so I end up with a green beanie with the springbok on the front. The springbok pattern is here:
Well, I’m not sure of exact numbers, but my husband’s head works well with the ones I do that measure about 6.5" from the lower edge to the start of decreases. Most likely that would be fine. If he has a large head maybe 7- 7.5" would work and if it’s tiny bit too tall it can just be slouchy.
That would probably be done with intarsia not fair isle. Intarsia is best done flat, but if you google or you tube it you can find it done in the round. More complicated though.
ETA: how you decrease depends on how many you cast on. That’s a pretty big pattern. Hmm…
Thanks @Jan_in_CA I was hoping to finish the pattern before starting the decreases to be honest, the wool will be my staple DK and the last time I measured a 10 x 10 cm swatch I think I had 24 rows . Also am I right in thinking that if you want 5 “wedges” you divide the stitches by 5 so it would be k2tog, k18 for example if you had 100 stitches?
When I’m browsing stitch patterns, I tend to try to stick with things that are 40 rows or fewer. That would be to be used starting after a brim of some type, and I’m usually working yarn thicker than DK. So I would say you’ll be fine with even some space above and below. (Me - I’d start the chart two or three rows after the brim, then allow for there to be more space above the art.)
Decreasing - yes, you can figure out how many wedges you want, divide the number of stitches by that, then work as you listed. However, most hats work with wedges of 10-12 stitches in order to get a nice rounded crown. You’ll be knitting decrease rounds quite a while if you start with k2tog, k18 and it might not be shaped as you want. With that many stitches, if you don’t want a lot of wedges, I’d look at doing the type of decrease that gives you more like pie pieces than a swirl. So, with 100 stitches, you’d have four wedges/triangles of 25 and you’d work in paired decreases coming from each side of the triangle. (E.g.: ssk, k21, k2tog, repeat four times for the first round of decreases. If you want 5 wedges, 20 stitches each, so ssk, k16, k2tog for the first round.)
(Rushing and this could be mud. Happy to clarify later. 
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The more wedges you have the more quickly it will decrease. The fewer wedges you have the more likely it will be taller and pointier. I’m assuming you want a rounded top? I would be more inclined to-
k8 k2tog, across row
Knit 1 row even
k7 k2tog, across row
etc
If you feel it needs to be a bit taller you can also put 2 rows even between the first few decrease rows then go to 1 row even. I’ve done both, but only by instinct not anything I can give as a real reason.
@Jan_in_CA yes rounded top! Is it always 1 less between the k2tog stitches per round? So k8, next round k7 then k6 etc? Also do you lose the same amount of stitches each time? So if you have 100 stitches and do k2tog, k8 and lose 10 stitches, will the k2tog, k7 round lose 10 stitches as well?
It’s amazing how much work to be done behind the scenes of a simple beanie!
Yes, always one less. You can make it easier on yourself to do two things.
On the first decrease row place a marker after each k2tog. Then the next time you decrease you just knit to two stitches before the maker and k2tog, slip marker, etc.
Look at the k2tog so you can recognize what it looks like visually. The base will look like two stitches (which it is). That way if you set your work down between rows you can look at your knitting and see what row comes next.
Once you learn how you will be able to design them easily even just in your head. I had to have an MRI a few years ago and to keep myself distracted I designed a hat. I came home and made it and this is the result.
http://www.ravelry.com/projects/JanCA/mri-hat
I’m getting quite good at finding them after that poxy snowman!! I’m quite good at undoing them as well… 
Thank you both so much, am quite excited about getting this one on the needles now!
you, that makes perfect sense, thank you!