How do I make it so that this script will deduct cash or the leaderstat?

Essentially you want to do something like this:

local cash = player.leaderstats.Cash
if cash.Value < 100 then return end -- player doesn't have enough money
cash.Value = cash.Value - 100

If you wish to make it so that it costs money for someone to buy a home, your script could look like this:

local debounce = false
local cost = 100
function onTouch(hit)
    if not hit.Parent or debounce then return end
    local player = game.Players:PlayerFromCharacter(hit.Parent)
    if not player then return end
    local cash = player.leaderstats.Cash
    if cash.Value < cost then return end -- player doesn't have enough money
    cash.Value = cash.Value - cost
    debounce = true
    local b = script.Parent.Parent:Clone()
    b.Parent = game.Lighting
    b.Name = "Home"..player.Name
    wait(.4)
    script.Parent.Parent.OwnerName.Value = hit.Parent.Name
    script.Parent.Head:Destroy()
    script.Parent.Parent["Home Owner: Nobody"].Name = "Home Owner: "..hit.Parent.Name
    script.Parent.Parent.Parent.Name = "Home"..hit.Parent.Name
    wait(3)
    debounce = false
end

script.Parent.Head.Touched:connect(onTouch)

Note, I made the following unnecessary changes:

• I took out if hit == nil then return end because hit can never be nil
• I merged some of the if statements and made it so that if any condition isn't met, the function returns early
• Some of the code was checking to see if the player had a character in the workspace. This isn't valuable, so I took it out.
• I updated deprecated functions (ex, use FindFirstChild, not findFirstChild; use Destroy() not Remove() -- alternatively you can use .Parent = nil if you want to re-use it later).

Instead of debounce = false, you might consider just removing the script (with script:Destroy()), since once you've removed the Head, this script can't do anything else.

Also note that the player will lose their money if the script fails (it shouldn't if you have everything set up correctly and if no other scripts might interfere). You could reduce this risk by taking out the wait(.4) and moving the cash reduction to right before the wait(3) currently is.