Somebody know software where i can design case for group buy?
The fact that you are starting off with that question is a massive red flag.
I get you have an idea and want to get it made, but CAD isn't like you download Final Cut and start splicing parts together. You can learn cad software on your own, Youtube will teach you, but to get to where you can make something presentable will take weeks and if you are not familiar with manufacturing methods the cost to make it can be ten fold. Not to mention you probably greatly underestimate the amount of time, money and effort this will cost. Machines have tolerances, there are multiple ways to do the same job, finding a shop takes time, waiting on that shop takes time because they will not prioritize you.
Don't be surprised if you spend the better part of a year learning, designing and waiting on the shop to make your first one, only to find it doesn't even come close to working and by the time you have a product you can actually offer up as a group buy that you've spent 2 years and spent $5-20k of your own money. Do you plan on eating that or adding it to the cost, don't forget finish (anodizing), packing and shipping. 50 cases is still a small batch for most shops so again you will be waiting, then waiting again at the anodizer, but while that's a small amount for them, it's not for you when you have to pack up 50 three pound items and delicately move them from the machinist across town to the anodizer then again to home where you get to box then take them to the post office to ship them.
You scoff at 2 years, but remember, you're starting from zero. You need to learn CAD, you need to find a shop, you need to wait for a hole in their schedule, fix your mistakes, tighten tolerances, make it look good, try and reign in costs, and then do it all again, multiple times. 2 years is not an outlandish number once you understand how long each step can take. If you had experience and a shop ready to take it on, you could knock it down to 3-6 months, but you have none of that.
But if you TRULY want to do this, Start with Fusion 360, buy a cheap ($20) digital caliper from Amazon or Harbor Freight (you WILL need one) and buy a 3d printer. Yes, the printer will be a hobby in itself and be another thing to learn but while learning the printer, you will be learning tolerances and design. The printer will pay for itself on the very first prototype. With it you can make and test your ideas (relatively) quickly and make sure you haven't made at least any colossal mistakes and come to an understanding of what you are working with. Meanwhile, start looking for shops and talking to people in the know to locate a reasonable shop and get direction on how to make minor changes that significantly cut the cost of manufacturing. You will still be into this a few grand before you have a good enough product you can offer for a group buy, but it will be faster and cheaper than the alternative.