A packed lunch

Lately, I have been cooking my lunch and bringing a lunch box to my the office lately to help reduce costs. It looks so hard, but I enjoy cooking. I cook it every Sunday for the week.(*) If I eat in the at a restaurant, ,  I sometimes can't sometimes freely select a menu freely. Because The kind of shops are limited shops near my office are limited, and almost of the meals are very expensive for me. If I cook lunch myself, I can choose the menu freely. So it's not hard, it's fun! In addition, cooking lunch myself makes helps to keep my body keep slender.

(*) depending on what you are trying to say -

I cook it every Sunday of the week. (means that I cook it each Sunday)

I cook it every Sunday.

I cook it every Sunday for the week. (prepare lunch on Sunday for Monday through Friday)

Comment:

It is very smart to prepare your own lunch; many places charge an arm and a leg for a mediocre meal. You can also have more free time during lunch and read a book in English. 

A packed lunch

Lately, I've been cooking my lunch and bringing a lunch box to my office lately to reduce cost to save money. It looks so hard, but I enjoy cooking. I cook it every Sunday for a week.* If I eat in the a restaurant, I sometimes can't sometimes select a menu freely,* because the kind of shops are limited near my office and almost ordering meals are is expensive for me. If I cook myself, I can choose the menu freely (or: I can customize my meals). So it's not hard, it's fun! In addition Also, cooking myself makes keeps my body keep slender.

*"I sometimes can't select a menu freely.." Do you mean you can't order what you want, or you can't customize your meal?

*"I cook every Sunday for a week." Do you mean you cook a week's worth of meals every Sunday?

Notes: Your writing is pretty good! I was able to understand a majority of it! Seeing that you might be a little advanced, make sure you don't get too wordy. You can see the strikethru's of the words I completely omitted, like "almost," "myself," and "makes." Be careful of sentence structures you create, such as "If I cook myself.." it literally translates to me as "I cook myself," as in, you're sitting in a pot of water, boiling yourself as food. :p The placement of "lately" in the middle of your sentence sounds like it's less powerful, put it to the front with a comma (I'm sorry I can't explain the reasoning behind this, sounds better in my opinion). "If I eat in the restaurant.." <--The reader thinks you're talking about a restaurant you already mentioned, make sure when you generally talk about a restaurant you use "a restaurant".

Great job! Good luck with your English lessons!