PRICE IS NEGOTIABLE
Create an inventory system with these tabs: Inventory, Skins, Trading, Shop, Market, and Gambling.
BTW: I have RK inventory, so if you want to build my system off of that I wouldn't mind that either.
Inventory will have slots for your primary and secondary weapon, a special item such as smoke grenade and throwing knifes, as well as a slot for your head, a helmet slot, your torso, your legs, and maybe feet as well. Add enough cosmetic items to make the pool seem random and large. Everyone starts with a default weapon of each type meaning no stat buffs and no mastery
Skins will have all the same slots as above, but the "skin" item you put in the slot will apply it's look to the weapon that it's sharing a slot with. Add enough skins to make the pool seem random and large. Also add dyes as an item and let you apply them to skins, changing item of the skin and the color it shows up on your equipment.
Trading will show you a list of all dead players (or all players if its pre round) and let's you send a trade request to them that will send them a chat message as well as display a window in the middle of the screen with a small timer that when it runs out it dissapears but the window shows the player who sent the message's icon and name and a "accept" and "decline" button. If they will accept it will then bring you into a chat that let's you trade weapons, skins, other cosmetics, OPs (oasis points, the currency for my server) and DDs (donator dollars).
Shop will have 2 sections with the second split into 2 as well. The first section will be buying crates, items which when opened will display a window that has a bunch of randomized items "spin" in a line until it slows down and lands on an item, then selecting random stats and mastery for the item if it's a weapon or special equipment, and giving you the item....
The rest I will tell you win you contact me because right now my fingers are sore from all my gaming today, I didn't talk about the randomized weapon system but I am assuming that part will be a lot of work as well.