What you need is a cutting mat, a clean work area, wooden skewers and toothpicks, a knife, superglue, plasticcard, filler and a file or sanding stick. Optional is a small saw and The Cutter, just cause it makes life easy for a scratchbuilder.
Get a piece of plasticcard of 40mm by 60mm
Draw lines to get this pattern. This will be your guide when putting down the basic shape.
Cut out some straight bits of plasticcard and make the basic shape. Don't worry about the height right now, this will get cut down later. What I forgot to do in this picture is add a few scraps of plasticcard to the inside corners for strength.
Cut some lengths of the wooden skewers, 1 a bit longer then the bunker is wide, 4 smaller ones with one end sanded smooth. This will be the logs for the front of the bunker.
Glue the lengths of skewer to the front of the bunker with superglue and let dry.
When dry, take a saw and cut at a 45 degree angle.
Repeat at the other end, this should be your result.
Add a small plasticcars triangle using the guideline drawn ealier and secure with superglue. Then cut ever smaller pieces of the wooden skewer, sanding down the tips and glue into place.
Repeat on the other side and you should end up with something resembling this.
Either with a knife or a saw, take off the top at the same level as the top of the skewer.
Glue down some plasticcard to make the roof.
Glue down 2 traingles of plasticcard. This will be the entry/exit point for your bunker. Make it wider then you normally wood as you will need to add the wood lining as well.
Cut down some of the toothpicks (these should be slimmer then the skewers) and glue these to the triangles.
Use scrap plasticcard or leftover sprue bits to fill out the sides.
Trim down the sides so you get a nice, if a bit bumpy, slope.
Use the toothpicks to cut smaller sections for the front of the bunker and glue into place.
I always use a nailclipper to round off the sides and then sand the entire adge. Get your own clippers for this, don't use the ones from SWMBO!! You can skip this step if you like it square.
Get a pot of your favourite filler. In my case, Black Lava from Vallejo cause it is just as coarse as the sand mix I use for my basework.
Spread the filler, let dry, repeat if needed and then they are ready for some paint. I'll let you get to grips with that bit on your own way.
I hope you enjoyed the tutorial and can put it to good use for yourself and on the battlefield. Remember, change the size of the base to create bunkers for other scales, bunkers tied in to other field positions and what not. Be creative.