How to fix players spawning on top of roofs/other players?

Put this script in ServerScriptService it disables player to player collisions

local PhysicsService = game:GetService("PhysicsService")
local Players = game:GetService("Players")
 
local playerCollisionGroupName = "Players"
PhysicsService:CreateCollisionGroup(playerCollisionGroupName)
PhysicsService:CollisionGroupSetCollidable(playerCollisionGroupName, playerCollisionGroupName, false)
 
local previousCollisionGroups = {}
 
local function setCollisionGroup(object)
	if object:IsA("BasePart") then
		previousCollisionGroups[object] = object.CollisionGroupId
		PhysicsService:SetPartCollisionGroup(object, playerCollisionGroupName)
	end
end
 
local function setCollisionGroupRecursive(object)
	setCollisionGroup(object)
 
	for _, child in ipairs(object:GetChildren()) do
		setCollisionGroupRecursive(child)
	end
end
 
local function resetCollisionGroup(object)
	local previousCollisionGroupId = previousCollisionGroups[object]
	if not previousCollisionGroupId then return end	
 
	local previousCollisionGroupName = PhysicsService:GetCollisionGroupName(previousCollisionGroupId)
	if not previousCollisionGroupName then return end
 
	PhysicsService:SetPartCollisionGroup(object, previousCollisionGroupName)
	previousCollisionGroups[object] = nil
end
 
local function onCharacterAdded(character)
	setCollisionGroupRecursive(character)
 
	character.DescendantAdded:Connect(setCollisionGroup)
	character.DescendantRemoving:Connect(resetCollisionGroup)
end
 
local function onPlayerAdded(player)
	player.CharacterAdded:Connect(onCharacterAdded)
end
 
Players.PlayerAdded:Connect(onPlayerAdded)