To make 4 year old play alone in room?

[Mrsknackered]

DS Aged 4 has the largest room in the house (the loft conversion) and has bloody loads of toys in there. Yet he refuses to EVER spend time in there.
He's fine going to bed, no fear of the dark but just refuses to play alone. Our living room is quite small and DS1 likes to play with Lego, playmobil, geomag etc and DS2 sees it as an opportunity to swallow tiny things.
Every evening when DS2 is in his cot I make an effort to play with DS1 in his room. We have just had a whole 6 weeks together. Today we went for a walk, made biscuits together, did play dough and I asked for 10 mins of him playing in his room (I was just in the bathroom on floor below and doors all open etc) and all hell breaks loose. It really jars me. He is under my feet all day just begging for TV/my phone. I told DM that I basically forced him to spend 10 mins in his room playing whilst I showered quickly (I had to shower, baby accident) and she thought it was really cruel.
AIBU to make him play in there?
I am so tempted to swap rooms with him as my coursework and sewing machine lives in piles on the floor whilst the largest room remains empty!

I would swap rooms with him if I were you. I don't think asking him to play in his room for a bit is the worst thing in the world but I was the same as your DS growing up. Kids don't want to be alone! It's natural. The only time dsd is alone in her room is when she's sleeping or tidying. Other than that I encourage her to he downstairs with us, and if I need peace and quiet I'll go to my room for a bit!

Yabu - he just wants to be close to you. He will start when he's about 6-7.

I think it is unrealistic to expect a 4 year old to want to go and play in his room on his own. I know, at that age, unless they were with a friend/brother, they always wanted to play in the same space as me. This doesn't mean I would always be playing with me though. My almost 7 year old chooses to play in his room sometimes. But at four, certainly my children, would see being sent to their room alone, as a punishment.
Could you allow him to bring down one toy at a time to keep on top of the clutter. Also, I used to use a unfolding baby pen as a fence to room divide baby away for older child's games. Worked really well.

YANBU, but I think you may have missed the window of opportunity for getting him used to it.

My DS would happily play in his room at that age as, once he outgrew naps at about 3 years old, he would have quiet playtime alone in his room for a couple of hours as DD was a dreadful napper and needed quiet, and that was the only way to achieve it. It had the upside of giving me time to catch up on a few jobs and have a cuppa in peace. So, when DD outgrew naps I insisted on her having quiet playtime if we were home during what had been nap time. She was always reluctant, but once it was forced on her she would play quite happily with her toys. I think it was actually really good for her to learn to be content in her own company as it didn't come naturally to her the way it did to DS.

Interestingly, a few months after starting reception year, she asked why didn't they have quiet playtime anymore as she missed it!

Yanbu.
I have always instigated chore/play since my dc were about 2. So I will play with them, then they play alone whilst I do a chore. Works for us.

Swap rooms! Why have a big playroom if he's not using it as one?

You are and are not being unreasonable! Lots of little ones play in the rooms, my 2 year old does, but if he doesn't want to then I wouldn't force the issue.

I feel bad because I don't want to upset him but sometimes just 15 minutes of him being in his room would be really handy just so I can get on with things.
He's quite happy to sit alone in front of a telly. Which means he is having more screen time than I would like.
The only reason I haven't moved rooms is because I don't like the thought of him being on the floor below just incase of a break in slightly paranoid

DD was about 10 before she'd choose to spend any time alone in her room. Not afraid, just liked to be with us. I think it's normal.

Ds didn't start playing in him room until he was around 10. He would get the toys he wanted to play with and bring them down. He's only 4 it's completely natural for him to want to be close to his family and not away in his room. Kids get under your feet YABU to expect otherwise at only 4, does he not go to school/nursery?

YABU he's 4, of course he wants to spend time with his parents when he can.

Yabu - set up an area nearby he can play but still be near you. Swap rooms if needed

My lo didn't enjoy time alone in her room until she was 6. Until then she was bloody velcroed to my leg. I'd swap rooms until he gets a bit older.

You wait come teenage years, he'll bloody love that room and you'll never see him!

Get a large blanket or similar for the living room and ask him to keep his lego on that, so at least you can scoop it all up in one go. I think you can get actual lego blanket bags. DS only started playing in his room aged 8. Toys all over his corner of the living room during the day and he had a bookcase with drawers in the living room to keep his things on/in.

And a wicker hamper and the drawers in the TV unit and the drawers in the 'good bookcase' and still bits of lego were all over the floor waiting to ambush people with no shoes on unless of course they had been already sucked into the hoover but that doesn't matter because all the lego is free and it doesn't matter if you lose a particular piece from a set.