$appPool = 'default'
Stop-WebAppPool -Name $appPool -Passthru
... deploy...

Start-WebAppPool -Name $appPool -Passthru
...deploy.....

or

$appPool = 'default'
Stop-WebAppPool -Name $appPool
while((Get-WebAppPoolState -Name $appPool ).Value -ne 'Stop'){
sleep 1 #second
}
... deploy...

Start-WebAppPool -Name $appPool
while((Get-WebAppPoolState -Name $appPool ).Value -ne 'Start'){
sleep 1 #second
}

...deploy.....