Weapon Card Creator: An amazing tool for making your own custom weapons
https://gamepro5.com/programs/tf2_weapon_card_creator/
I use it for all my creations and I think its the main thing they use in the subreddit too, give it a try its pretty easy to use!
This is a good place to get ideas too (even if reddit sucks): https://www.reddit.com/r/TF2WeaponIdeas/
I mean dont just ripped them off and post them here but it can give you some ideas on how to make tf2 weapons, ideas for weapons and what not