I've had both indoor cats and those who like their freedom via the cat flap.
I think you have to weigh up the pros and cons very carefully.
If you live by a main or busy road - forget it. Keep your cat indoors.
Outdoor cats do run the risk of being chased by other animals (usually dogs), fighting with other cats and there is always the risk that someone might see the cat, think "Oh, what a lovely cat. I'll take it home" and you never see your cat again.
That nearly happened to my neighbour's cat earlier this year. As it turned out, it was a sweet story but gave my neighbour such a scare. Her cat is getting on a bit and she usually stays in the garden or sits at the front gate. She always comes in when she's called.
One day, she didn't. My neighbour asked if I'd seen her cat. No, but I'd keep a watch out for her. The next afternoon, I'd just come home from work when my neighbour came out. She'd got her cat back.
I turned out that a little girl - she's about 9 years old had lost her cat (illness I think) and she'd been pining for her furry friend. Seemingly, they'd only moved into the next street a few days previously but the little girl had made friends with some of the children in our street. She spotted my neighbour's cat and decided to sneak her home. Her mother found out when she heard miaowing coming from the little girls bedroom, went to investigate and found my neighbour's cat. She promptly took my neighbour's cat back, apologising profusely. What the lady didn't realise, that her daughter was missing her feline friend very much. The cat had been there long before the little girl was born, so she had grown up with the cat.
They had had their cat a long time and hadn't planned on getting another but that weekend they decided to adopt another cat. I'm sure that little girl is loving her new cat very much.
As far as outdoor cats being more prone to catching diseases, I know by experience that that is not always the case. If you plan to let your cat out, make sure all vaccinations are up-to-date. At least here in the UK, we don't have a Rabies problem which is something else to consider.
I'm afraid I do not agree with Kittilove4 (sorry Kittilove4). Cats are, by nature and what they are, very much outdoor animals. Indeed, here in the UK they are still (wrongly IMO) classed as wild animals but they adapt very well to living inside. There isn't a cat I've ever come across who prefers cold and wet to curling up infront of a cosy fire or claiming your lap to sleep on

Like I said, some of mine are indoor/outdoor cats and others indoor cats. My late Lucy was 22 years old when she passed to RB just over a week ago. She was an indoor cat only due to her being crippled. Even so, it didn't stop her nearly dying from cat flu 5 years ago. It took us all by surprise, even our vet but he said she'd probably had it as a kitten and it can lie dormant for years, maybe never even rear it's head again or can flare up.
My two half-Bengals are indoor cats only. They are beautiful and I'm sure they would disappear quickly if I let them out. We are getting a half-Siamese beauty soon and he will also be an indoor cat. I intend to train him on a harness and lead.
I'm very lucky where I live. We have a 20mph speed limit and our road is a dead-end so cars tend to come down very slowly. Most of us have cats and there are always a lot of young children playing in the small field to the front, so we are vigilent.
To the rear of my house there is a cats playground - a woodland full of interesting things to do and see for the cats. I used to get an abundance of little presents from there - anything from mice, rats, frogs, toads, birds to the two most unusual "gifts" from my cats - a mole and a squirrel tail. What happened to the rest of the squirrel, I haven't got a clue.
Since Lucy's passing, my oldest cat is now Blue who is 15/16 years old. He has the freedom to go in and out as he pleases but these days prefers to stay in, only going out to do what he has to do and coming back in. In winter he refuses to go out at all so we always put a litter box for him.
At the end of the day, it is your cat, not your room-mates so it is your decision.
If you have a large enough yard or garden, a good compromise would be to build a run for your cat.