Generate add / alter script for missing / different type columns

Select 
'if not exists(select * from dbo.sysobjects so left outer join dbo.syscolumns sc on (so.id=sc.id)
  where (so.id = object_id(N''[dbo].['+t.name+']'')) and (OBJECTPROPERTY(so.id, N''IsUserTable'')=1) and (sc.Name=N'''+c.name+''') )
    ALTER TABLE '+t.name+' ADD [' + c.name + '] ' + ty.name + (CASE WHEN ty.name like '%char%' THEN '('+(CASE WHEN c.max_length<0 THEN 'MAX' ELSE CAST(c.max_length/(CASE WHEN ty.system_type_id in (231,239) THEN 2 ELSE 1 END) as nvarchar) END)+')' ELSE '' END) + (CASE WHEN c.is_nullable=1 THEN ' NULL' ELSE ' NOT NULL' END)+'
GO

if exists(select * from dbo.sysobjects so left outer join dbo.syscolumns sc on (so.id=sc.id)
  where (so.id = object_id(N''[dbo].['+t.name+']'')) and (OBJECTPROPERTY(so.id, N''IsUserTable'')=1) and (sc.Name=N'''+c.name+''') and ((sc.xusertype<>'''+CAST(ty.user_type_id as varchar)+''') or (sc.length<>'''+CAST(c.max_length as varchar)+''')))
    ALTER TABLE '+t.name+' ALTER COLUMN [' + c.name + '] ' + ty.name + (CASE WHEN ty.name like '%char%' THEN '('+(CASE WHEN c.max_length<0 THEN 'MAX' ELSE CAST(c.max_length/(CASE WHEN ty.system_type_id in (231,239) THEN 2 ELSE 1 END) as nvarchar) END)+')' ELSE '' END) + (CASE WHEN c.is_nullable=1 THEN ' NULL' ELSE ' NOT NULL' END)+'
GO

'
from sys.tables t
LEFT JOIN sys.all_columns c on t.object_id=c.object_id
LEFT JOIN sys.types ty on ty.user_type_id = c.user_type_id
Order by t.name, c.column_id