My g/f has been trying to change my style for some time now. She complains that I never wear anything preppy or casual. She feels the only way that I would benefit from her actions is for her to lay out my clothes. She feels that the only way she could do this without me putting up an argument is to ask me to go take a nap and while I'm taking a nap she lays out the outfit. She has been laying out crew neck cardigan sweaters with nice slacks. When I have worn the cardigans, she has to critique the sweater before I get the chance to button it up. She feels as part of her critiquing of the outfit is to button up all of the buttons herself.
She does the same for polo shirts as well, she feels it necessary to button them as needed. I have no problem letting her pick out the clothes, taking a nap as needed but is this going too far

Can you say Control Freak?
That is taking it a bit far. I like for my husband to look nice and buy most of his clothes (he doesn't have the time anymore). But, I would never dress him. He's a grown man, he can do it himself.
The only real directive he gets is when we are going some where that might require him wearing something other than jeans.

You can dress yourself. You need to tell your girlfriend this. You are grown, not a child that can't button his shirt.
Did she not get enough of "dress-up" time as a child?

I would never tell my boyfriend what to wear, let alone dress him! I do ask him to dress nice on occasion, like if we are going out with my friends or something. He is a jeans and t-shirt kind of guy, so sometimes I do need to remind him that he needs to dress up for some events. But, I just remind him to wear something nice (like if we are going to my grandma's for Thanksgiving or something), I don't pick out the clothes.

I started doing the clothes shopping for both of us (we live together) because he asked me to since he HATES to shop. But, I know what he likes and buy him mostly casual clothes, with a few mix and match nice outfits.

I think your girlfriend is taking it a little too far, personally. Telling you when to take a nap and telling you how many buttons to button up is a little obsessive.

Tell her you think she has a great sense of style, and that you love her ideas, but you are a grown man. Tell her that while you appreciate her help in co-ordinating outfits, you will make your own decisions regarding buttons, sweaters, and nap time. She is kind of treating you like a little kid. If you tell her about it now, she might get mad, but it's better to let her know how you feel now rather than later. Hope this helps!

My daughter is like that to a degree. It is a control freak thing AND an I don't want to be embarrassed with anything under MY standard of style.
If you like the polo's and cardigans and wearing them when she says then let her pick out your clothes. But tell her you will wear the clothes the way that makes you feel comfortable.
You are grown and don't need a mother to smother.