Cannot find what I want so I want to combine patterns

[Bertaberta]

I just wondered where one turns for patterns when they cannot find what they are looking for.     I want to make a heavy and a little bulky sweater type coat but I want the collar to be higher in the back, sleeves to be snug at the wrists, with pockets and extend mid thigh.  I am leaning toward a Tunisian afghan hook (will be my first attempt) but.... cannot find a video or book or know of anyone who has any insight.  Any ideas appreciated. 

[Granny Square]

Hi Bertaberta.  I'm not remotely a Tunisian stitch expert (have only done pot holders and entrelac, not garments or shaped things), but most of what you mentioned sound not-hard (in not-Tunisian crochet) if 'patch pockets' are OK with you (ones set in a seam are not difficult, but  a bit trickier in the 'getting-your-mind-around how it goes together' way).  Length is just a matter of adding or subtracting rows.  To draw-in the cuffs, I'd work the sleeves cuff-up and use plain SC ribbing, which is SC in the back loop across the depth (meaning, 3" for a 3" cuff) for a length (around your wrist), seam the short ends into a tube, then crochet into the opening to make the sleeve.  

I'm assuming by saying 'Tunisian hook' you meant  'Tunisian family of stitches', right?  Because a non-Tunisian stitch with those hooks would be a pain in the fanny wrist.

How much experience do you have using Tunisian stitches?  Clothing patterns using Tunisian stitches are not common.  Example, doing a search on Ravelry, there are 5457 crochet cardigan patterns (those may not all be still in print, or in English), but only 120 using Tunisian stitches.  And only 16 are free, and 3 of those are baby sized.  And only one is particularly coat-like (and...it's out of print).

CrochetKim (Kim Guzman) is a Tunisian expert, has published a lot of books and patterns and has tutorials you might want to look at for techniques.  https://crochetkim.com/free-patterns/technique/tunisian-crochet/  However, in cross checking patterns on Ravelry, there was a pullover but nothing coat-like in her patterns.

[Granny Square]

This was the only solid pattern, bulky yarn, free, button up, and collar pattern I could find (not Tunisian)

https://www.garnstudio.com/pattern.php?id=3387&cid=17  ('Eskimo' is super bulky, put-up is 55 yards, 50oz/per skein; "Highlander" is  also super bulky, 88 yards per 50 gram skein. You will need to convert the grams in the pattern to yards, and buy however many skeins you need to get the yardage.