you can use the plater ceiling type aluminium profile like what shared by mrkang.
I personally used SMD2835 120LED 24v strip, but take note your profile has to be at least 1cm deep, or else you will have dark spots, or you could go with the COB type LED strip but these are slightly dimmer compared to the 2835 120LED 24v.
Just go to those lighting shop to see the LED strip then you would have an idea, tell them 2835 120LED 24v then they will show you.
Also, if you're doing squares like me, it should be a ring connection to the power supply so you would lose brightness towards the end of the strip, you'd get more even brightness

mine was about 12 meters, if you're worried about ring connection being insufficient, you can try using 2 power supplies at opposite corners and create L shapes from each corners, thus each power supply is powering 2x 3.75m strips