How to place a block with the mouse using mouse.Hit.Position?

I'm not having errors and it works, but it's really finicky. I have a LocalScript to do all the math and everything and then I send it through an event to place it with a ServerScript. I was hoping someone could improve my code to make it better. Here is the LocalScript inside StarterGui

local uis = game:GetService('UserInputService')
local plr = game.Players.LocalPlayer
local mouse = plr:GetMouse()

if uis.MouseEnabled then
    local OriginalMousePos = mouse.Hit.Position
    mouse.Button1Down:Connect(function()
        if plr.Mode.Value == 'Building' and plr.Block.Value ~= '' then --Mode is the mode they are in (None, Building, or Removing) and Block is the block they are using (string of the block's name)
            local pos = mouse.Hit.Position
            local x = math.floor(pos.X)
            local y = math.floor(pos.Y)
            local z = math.floor(pos.Z)
            local bs = plr.BlockSize.Value --Size of the block
            local base = workspace.Plots[plr.Plot.Value].Bases.Base --base they are building on
            local downX = base.Position.X - (base.Size.X / 2)
            local upX = base.Position.X + (base.Size.X / 2)
            local downZ = base.Position.Z - (base.Size.Z / 2)
            local upZ = base.Position.Z + (base.Size.Z / 2)
            local coords = Vector3.new(x + bs/2, y + bs/2, z + bs/2)
            if coords.X > downX and coords.X < upX and coords.Z > downZ and coords.Z < upZ then --Make sure they are in they're plot
                game.ReplicatedStorage["Remove Passive"]:FireServer() --remove any pasiive blocks on the base
                game.ReplicatedStorage["Place Block"]:FireServer(plr.Block.Value, coords, bs, false) --place a block
            end
        end
    end)
    while true do
        wait()
        if OriginalMousePos ~= mouse.Hit.Position and plr.Mode.Value == 'Building' and plr.Block.Value ~= '' then --If they still have the same position, there is no point in placing another passive block
            local pos = mouse.Hit.Position
            OriginalMousePos = pos --update OriginalMousePos
            local x = math.floor(pos.X)
            local y = math.floor(pos.Y)
            local z = math.floor(pos.Z)
            local bs = plr.BlockSize.Value --Size of the block
            local base = workspace.Plots[plr.Plot.Value].Bases.Base
            local downX = base.Position.X - (base.Size.X / 2)
            local upX = base.Position.X + (base.Size.X / 2)
            local downZ = base.Position.Z - (base.Size.Z / 2)
            local upZ = base.Position.Z + (base.Size.Z / 2)
            local coords = Vector3.new(x + bs/2, y + bs/2, z + bs/2)
            if coords.X > downX and coords.X < upX and coords.Z > downZ and coords.Z < upZ then --Make sure they are inside the base
                game.ReplicatedStorage["Remove Passive"]:FireServer() --remove any passive blocks
                game.ReplicatedStorage["Place Block"]:FireServer(plr.Block.Value, Vector3.new(x + bs/2, y + bs/2, z + bs/2), bs, true) --place passive block. 
            end
        end
    end
end

If you are wondering why I added half the size of the block when firing the event to place the block, it's to center the block on the plot.

If you need it, here are the scripts for placing a block and removing a passive. Placing a Block in ServerScriptService

local PS = game:GetService('PhysicsService')

game.ReplicatedStorage["Place Block"].OnServerEvent:Connect(function(plr, block, coords, bs, passive)
    local block = game.ReplicatedStorage.Blocks[block]:Clone()
    block.Position = coords
    block.Size = Vector3.new(bs, bs, bs)
    if passive then
        block.CanCollide = false
        block.Transparency = 0.5
        block.Name = 'Passive'
        PS:SetPartCollisionGroup(block, 'Building')
    else
        PS:SetPartCollisionGroup(block, 'Built')
        plr.Blocks[block.Name].Value = plr.Blocks[block.Name].Value - 1
        plr.Refresh.Value = true
    end
    block.Parent = workspace.Plots[plr.Plot.Value].Blocks
end)

Removing a Passive in ServerScriptService

game.ReplicatedStorage["Remove Passive"].OnServerEvent:Connect(function(plr)
    pcall(function()
        workspace.Plots[plr.Plot.Value].Blocks.Passive:Destroy()
    end)
end)

Thx in advance