I like D&D 5e, but even with homebrew it can't really accommodate for my ideas. So I'm going to make my own system. Any tips and ideas? 

Take things slow. Ive also started writing my own, and Im 100 pages through after 1 month. Im personally fine cause TTRPGs are all I do with my life, but thats enough to give a lot of people burnout. Just remember to not go too quick on the workload for your own sake

You may want to check out this video.  He's talking about the principles of Game Design and using D&D and what he sees as its inadequacies for a foundation for "gun play" so to speak, so then does a sort of off the cuff, or apparently off the cuff, think through as to what a game supporting an old west mythic gunslinger style firearms combat system would need.  It's a good vid.

EDIT: would help if I actually put the vid in here, right?

I would first of all note down what it is you're trying to achieve that 5th Edition doesn't let you, before reading and playing other TTRPG systems before making your own, unless it's absolutely bare bones (a friend of mine ran a one-shot with pre-generated characters and a single d6). If your entire game design experience orbits around your time with 5E, your system is going to be little better than a fantasy heartbreaker, which I guess is fine if it's solely for personal use. Just be careful, as ChristheSoulcasterMage rightly says, you don't want to burn yourself out when you could quite simply use a different system better suited for your needs.

If you want inspiration I'd recommend checking out r/rpgdesign, the Angry GM and the Alexandrian.

Quote from HexTherapy >>

I would first of all note down what it is you're trying to achieve that 5th Edition doesn't let you, before reading and playing other TTRPG systems before making your own, unless it's absolutely bare bones (a friend of mine ran a one-shot with pre-generated characters and a single d6). If your entire game design experience orbits around your time with 5E, your system is going to be little better than a fantasy heartbreaker, which I guess is fine if it's solely for personal use. Just be careful, as ChristheSoulcasterMage rightly says, you don't want to burn yourself out when you could quite simply use a different system better suited for your needs.

If you want inspiration I'd recommend checking out r/rpgdesign, the Angry GM and the Alexandrian.

 OK so I'll be more specific if that helps.

My basic premise is: A world of floating islands and endless skies is just starting to recover from a horrific war. The technology is roughly WWII-ish, with dieselpunk planes and airships of all shapes and sizes. There is currently a cold war between two major powers, and a rump state left over from a huge empire which is bitter after a period of revolutions where almost all their territories became independent. Worryingly, this cold war is on the brink of becoming... not so cold, and the two sides are developing new weaponry which might be too powerful for their own good.

The players will be the crew of their very own airship, each with their own unique role. The classes I have so far are: Pilot, Navigator, Gunner and Mechanic. Any ideas what else I could do? I want at least 5 or 6 classes. They will work together to triumph in aerial dogfights and negotiate with NPCs on the islands. They will also be able to customise, modify and upgrade their plane. I'm not sure what stats they'll have and how the aerial dogfights will work.

Quote from TheFlamboyantGnome >>

Quote from HexTherapy >>

I would first of all note down what it is you're trying to achieve that 5th Edition doesn't let you, before reading and playing other TTRPG systems before making your own, unless it's absolutely bare bones (a friend of mine ran a one-shot with pre-generated characters and a single d6). If your entire game design experience orbits around your time with 5E, your system is going to be little better than a fantasy heartbreaker, which I guess is fine if it's solely for personal use. Just be careful, as ChristheSoulcasterMage rightly says, you don't want to burn yourself out when you could quite simply use a different system better suited for your needs.

If you want inspiration I'd recommend checking out r/rpgdesign, the Angry GM and the Alexandrian.

 OK so I'll be more specific if that helps.

My basic premise is: A world of floating islands and endless skies is just starting to recover from a horrific war. The technology is roughly WWII-ish, with dieselpunk planes and airships of all shapes and sizes. There is currently a cold war between two major powers, and a rump state left over from a huge empire which is bitter after a period of revolutions where almost all their territories became independent. Worryingly, this cold war is on the brink of becoming... not so cold, and the two sides are developing new weaponry which might be too powerful for their own good.

The players will be the crew of their very own airship, each with their own unique role. The classes I have so far are: Pilot, Navigator, Gunner and Mechanic. Any ideas what else I could do? I want at least 5 or 6 classes. They will work together to triumph in aerial dogfights and negotiate with NPCs on the islands. They will also be able to customise, modify and upgrade their plane. I'm not sure what stats they'll have and how the aerial dogfights will work.

 If you don’t want to go through the work of creating your own system, I’d suggest checking out a system called Cogent Roleplay. It’s pretty simple and very honest friendly, plus it’s free! Just look up Cogent Roleplay and you should find the website. 

I have no experience making my own system so that’s ask I have to offer. 

Well thanks anyways, I'll check it out.