The error given is: Workspace.REventHandler:3: attempt to index local 'item' (a nil value)
Local Script which defines item "selectedItem's value is set to 1 and there is always a child in foundation"
local items = game.Lighting.items:WaitForChild("foundation"):GetChildren()
local item = items[stat:WaitForChild("selectedItem").Value]:Clone()
mouse.Button1Down:connect(function()
if stat.isValid.Value == true then
evt.build:FireServer(item:GetPrimaryPartCFrame(),
items[stat.selectedItem.Value]:Clone())
end
end)
game.ReplicatedStorage.REvents.build.OnServerEvent:connect(function(plr, cframe, item)
item:SetPrimaryPartCFrame(cframe)
item.Parent = workspace.targetFilter.building
end)

3 comments
Try this: items:WaitForChild(stat:WaitForChild("selectedItem").Value)
And don't use lighting for storage.
Those things are not loaded when localscript begins so use WaitForChild.