My son does not allow me to read any NEW book or magazine and always becomes cranky till I stop reading and hand over that book to him.
Initially I thought it might be temporary thing but now, it has become a ritual.
How do I deal with it?
My immediate impression is that it's a power struggle. He wants your attention. He wants you to play with him. He sees your reading material as the thing that is keeping you from interacting with him.
Unless your new material is suitable for children (and you don't mind it being torn etc.) then don't give him your things. Instead, put them away and play with him.
I don't have much time for myself at home while the kids are awake either. I accept this as a phase in their lives - and in my life. Forget about computer time, books, magazines - until after bedtime. That's time for yourself.
Once he grows older, he will learn to respect your time needs too. But 4 is too early for that. Accept it.
Depending on when my kids finally fall asleep, I have anywhere between zero and two hours for myself, but this time is normally not spent reading or with TV because there's grown-up stuff to do in the household -- maintenance, planning, preparations. Actual play time for myself is a rare and special treat... I'm sure that once my smallest son is old enough to be able to safely entertain himself for an hour or so, time for myself becomes available again.
I try to think of the challenging time until then as an investment... effort now pays off later. It's probably not wise to draw too strong parallels between children and investments (long-term break even?) but it helps to realize that small children grow up and I should enjoy their childhood as much as I can!
Between two and five or so, kids are really testing out their impact on the world around them. They still also need a lot of time with you. They spend a lot of time asserting their own opinions and desires over the people around them and test the limits of what they can effect. Without all the verbal skills you have, especially related to emotions, they often turn to other means to get what they want. This is all done at only a sub or semi concious level, it is not as though they are thinking, "how can I manipulate mom and dad this time?" but they are learning new skills related to cause and effect and what effect they can have and testing those skills. This manifests itself in different ways and generally by the time they are four or five things are calmer than at two and three, but your child is reaching new levels of sophistication in his/her exertion of control.
Additionally, kids often just want what you have because you have it (you are pretty cool after-all) so when you combine this fact, with the fact that they are testing how much influence they can have, you have kids that get "moody" until they get what they want. I have taught both preschool (two to four years old) and Middleschool (adolscent years) and always laughed when people asked how I could switch from one to the other so easily - its the same thing! Older kids just have a bigger vocabulary of "bad words" and "moody tactics" (well, and the ability to deceive).
I suggest a three-fold approach:
Offer up opportunities for your child to exert control in healthy ways that you aren't already. For example, let your child choose what he will wear every morning by offering two - three options that are all weather appropriate. Let your child choose between two or three things frequently throughout the day and when-ever possible. Set clear boundaries for the things about which your child has no choice and stick to it on those things (for example, bedtime is hard and fast, but he can choose whether he brushes his teeth first or puts his pj's on first). This allows your child to feel in control of some aspects so he is less likely to get "moody" with you.
Just in case your child is simply wishing for more time to spend with you and really wants you to stop reading and play instead, before you read your own book or magazine to yourself, read a few with your child to be sure he has had his time with you. At the age of four, your child really does want to simply spend time with you. Most of your adult reading will probably happen when he is asleep etc. However, seeing you read to yourself once in awhile is a healthy thing for kids as it helps them to enjoy reading as well. While you read with him, model how to turn pages gently and what appropriate treatment of these tools looks like. At four, he can learn how to use books and magazines without ruining the pages. Then, make sure to offer your child a magazine of his own to look at while you look at yours. There are some wonderful kids magazines out there like Ladybug and Highlighters, Ranger Rick, Zoo News. . . It doesn't have to be new everytime, but offer up something so he can read alongside you.
When your child is using the tactics you refer to as "moody or cranky," state very simply, "I understand you want the magazine, but you have spoiled many of my magazines and books. When you demonstrate you know how to care for them, we will talk again." Then, be a broken record. Just repeat this refrain if he grabs at the book, argues with you, asks for it again, throws a tantrum, etc. You can even repeat the refrain and add, "X behavior is not the way to get what you want." If your child's behaviors persist, offer up a consequence suitable to his behaviors.