Adding primary key using designer in SQL would take you so much time.
Here's a script that would automatically list all the tables without a primary key and create one. You can also filter by schema.

List all tables without Primary Key 

select   

a.table_name, 

a.column_name,

a.ordinal_position

from information_schema.columns as a

inner join sys.tables as b on a.table_Name = b.name

where ordinal_position <= 1 

and (object_id not in(SELECT object_id from sys.indexes WHERE is_primary_key=1))

Add Primary key

DECLARE cur CURSOR FOR 

select   

a.TABLE_SCHEMA as sn, 

a.table_name as tn, 

a.column_name as cn 

from information_schema.columns as a

inner join sys.tables as b on a.table_Name = b.name

where table_schema in(schema names) and  

ordinal_position <= 1 and 

(object_id not in(SELECT object_id from sys.indexes WHERE is_primary_key=1)) and  

substring(a.column_name, len(column_name)-1, 2) = 'Id' 

DECLARE @sn sysname,

@tn sysname, 

@cn sysname, 

@sql varchar(500) 

OPEN cur     

FETCH NEXT FROM cur INTO @sn, @tn, @cn 

WHILE @@FETCH_STATUS = 0     

BEGIN 

SET @sql = 'ALTER TABLE [' + @sn + '].['+ @tn +']  ADD  CONSTRAINT [PK_' +@tn +'_'+ @cn+ '] PRIMARY KEY CLUSTERED

(['+ @cn+'] ASC) ON [PRIMARY]'    

PRINT @sql   

exec (@sql)  

FETCH NEXT FROM cur INTO @sn, @tn, @cn     

END 

CLOSE cur     

DEALLOCATE cur

 

Happy coding ;)