Hi, My baby has rolled twice from back to front and is 3.5 months. He rolled front to back when 3momths so he is now unswaddled. I was reading it’s time to move to cot although the cot cannot fit in our room ? So therefore I cannot sleep next to him. What’s the best option ? Thank you

Red Nose does recommend moving baby from a bassinet to cot (as well as arms out of swaddle) when rolling.
It is important that baby has the space of a cot & arms free to roll safely.
Most babies will be rolling over by 4- 5 months - some earlier. This is very normal as babies grow & become stronger.
Many babies then prefer to sleep on their tummy.
This is not something that needs to be stopped. It is important to make his new environment as safe as possible.

Also, ensure that the cot mattress is firm & flat & there is nothing soft or loose in the cot,
Always continue to place baby on back to sleep.
Increasing tummy time when awake.
https://rednose.org.au/article/what-do-we-do-now-that-a-baby-has-started-to-roll-over

Many parents use a bassinet for the first few months to facilitate room sharing.

Red Nose does recommend Room Sharing for the first 6 - 12 months as a way of reducing the risk of Sudden Unexpected Death in Infancy (SUDI)

However, the baby’s sleep environment would take priority over room sharing.
Most bassinets are unsuitable for babies beyond 3-4 mths of age & a cot is important once baby is rolling.

Red Nose has the following information

Parents are not expected to observe their baby constantly. 
If your baby is sleeping in a separate room check baby regularly to ensure that the baby remains on the back and the head and face remain uncovered (as baby grows beyond 5-6 months they will move around the cot and roll over; settle baby to sleep on their back but let them find the sleep position they feel most comfortable in. 

A safe cot and safe sleep environment is still necessary for babies older than 5-6 months)
The protective effect of room sharing can be partially explained by increased adult supervision and observation of the baby.

Room-sharing facilitates a rapid response to a baby’s needs, and supports breastfeeding, and is more convenient settling and comforting of babies. It also provides closer mother-baby contact and communication
https://rednose.org.au/article/room-sharing-with-baby