You should just buy it from the shop... you won't have to worry about the nutritional content.. and it won't go off or go mouldy.
If you want to have some fun making your own.. you can feed your home made food as a treat... as it is bound to taste better than the boring normal food lol.
Don't add sugar to your mix or oyster shells... too much calcium is dangerous for growing chicks. And they don't need lots of sugar.
Here is an idea for a mix.. I used for my sick chickens and as a treat for my parakeets and other cage birds.......
Hard boiled egg with shell
Finely chopped broccoli
Finely chopped carrots
Put all this in a bowl and smash it all up together until its like fine crumbs. Make is quite dry.. not mushy.
You can make a big batch and freeze it.. and then just take out and de frost what you need that day.
Only leave this in the cage for a short time as it will go off quickly as its fresh.
You could even add other stuff.. like dried mealworms or fish food. You can get some good ideas on line.... just don't add any grains.. as the chicks won't be able to digest them without grit and they don't have enough protein for growing chicks.